High frequency heating apparatus for providing a uniform heating of an object

ABSTRACT

A high frequency heating apparatus for heating an object to be heated is provided with an electromagnetic wave emission means for emitting electromagnetic waves, a local heating means capable of heating an optional portion of the object by the electromagnetic waves emitted from the emission means, and a control means for controlling the local heating means. The high frequency heating apparatus is further provided with a stage on which the object is placed, a protecting means for protecting the local heating means, a setting means and a detection means, so that the local heating means, the electromagnetic wave emission means or the stage is controlled in accordance with the setting means or the detection means.

TECHNICAL FIELD

The present invention relates to a high frequency heating apparatus forheating objects to be heated such as food or the like.

BACKGROUND ART

A microwave oven as a representative high frequency heating apparatushas conventionally been constructed as shown in FIGS. 1-7.

A microwave oven of FIG. 1 is of a general structure employing aturntable 1. In this microwave oven, electromagnetic waves emitted froma magnetron 2 as an electromagnetic wave emission means are transmittedvia a waveguide 3 to a heating chamber 4, where the waves aredistributed as standing waves that are determined by the shape of theheating chamber 4 and the position of an opening 5 through which theelectromagnetic waves are radiated into the heating chamber 4. A food 6generates heat correspondingly to an electric field component of thestanding waves and a dielectric loss of the food 6. The electric power P[W/m³ ] absorbed per unit volume of the food 6 is expressed by theintensity of an applied electric field E [V/m], the frequency f [Hz],the dielectric constant εr and the dielectric tangent tanδ of the food 6in an expression (1) below. The heating distribution of the food 6 isgenerally determined by the distribution of the standing waves of theelectromagnetic waves and, hence, the heating distribution on concentriccircles is uniform due to a rotating of the turntable 1.

    P=(5/9).εr.tan δ.f.E.sup.2 ×10.sup.-10 [W/m.sup.3 ](1)

In FIG. 1, reference numeral 19 denotes a control means, 22 denotes amotor, 23 denotes a weight sensor, and 27 denotes a fan.

As other examples of the uniforming means, a stirrer system has beenemployed in which electromagnetic waves are stirred by a constantrotation of a metallic plate inside the heating chamber. Electromagneticwaves are also taken out from the waveguide 3 by a rotary waveguide(emission part) 8 having a coupling part 7 and are emitted through anemission port 9, as shown in FIG. 2, in other words, the opening partitself has been rotated constantly. In this case, the rotary waveguide 8has been built on a bottom face of the heating chamber 4 and rotatedconstantly at all times by a motor 10, and the whole of a bottom part ofthe heating chamber 4 has been covered with a cover 11 of a materialallowing the electromagnetic waves to pass therethrough.

Actually, however, most of the apparatuses in the market are of theturntable type.

Some apparatuses are provided with a plurality of opening parts, whereinan exit for the electromagnetic waves is switched to provide a uniform aheating distribution. FIG. 3 shows an apparatus of the kind having twoopenings 5 defined in a side wall of the heating chamber 4 (JapanesePatent Laid-Open Publication No. 4-319287).

A plurality of magnetrons and a plurality of waveguides are installed insome cases to constitute a plurality of opening parts (Japanese PatentLaid-Open Publication Nos. 61-181093 and 4-345788).

Alternatively, one waveguide is branched in many directions to form aplurality of waveguides while there is arranged a single magnetron,thereby constituting a plurality of opening parts (Japanese PatentLaid-Open Publication No. 61-240029 and Japanese Utility Model Laid-OpenPublication No. 1-129793).

In a different constitution, end faces 14 of two sub waveguides 13 aremoved at positions facing a plurality of openings 5, as indicated inFIG. 4, so that the electromagnetic waves may be directed to one opening5 which apparently is easy for the electromagnetic waves to passthrough, to thereby uniform the heating distribution (Japanese PatentLaid-Open Publication No. 5-74566).

In a system of FIG. 5, a metallic part 12 is moved within the singlewaveguide 3 having a plurality of openings 5, so that the opening 5,which apparently is easy for the electromagnetic waves to pass through,is selected to thereby uniform the heating distribution (Japanese PatentLaid-Open Publication Nos. 3-11588 and 5-121160).

In FIGS. 6 and 7, a plurality of openings are formed at upper and lowerparts of the heating chamber, and the openings 5 at the lower part areswitched to thereby provide a uniform heating distribution (JapaneseUtility Model Laid-Open Publication No. 1-129793).

A feedback control is also executed in some apparatuses by detecting theweight, shape, temperature or dielectric constant of the food 6 or thetemperature, humidity or electric field in the heating chamber bysensors.

According to the above-described conventional arrangements, however, inthe case where the waveguide and the heating chamber are connected toguide the electromagnetic waves into the heating chamber, all kinds offood could not be heated uniformly by a single opening part, because theposition of the optimum opening part to obtain a uniform heatingdistribution was different for every material or shape of the food.

For example, when a flat food is heated by the conventional microwaveoven, the heating proceeds from an edge portion of the food, resultingin a large heating irregularity with a central portion of the food leftcold.

Considering the position of the opening part, if the opening part isformed near the center of the bottom face of the heating chamber andwhen a bottom face of the food is heated, the food is uniformly heatedif it is a liquid one allowing convection, whereas only the bottom faceof the food is raised in temperature if the food is a solid one allowingno convection. In this case, while the concentric heating distributionis made uniform with the use of a turntable, the heating distribution ina radial direction or a vertical direction as viewed from a rotationalcenter of the turntable cannot be improved in spite of the rotation ofthe turntable.

When the stirrer or rotary waveguide is used to stir the electromagneticwaves, the electric field distribution is changed in such a manner as toswitch the opening part in accordance with the rotation of the stirreror rotary waveguide and, hence, the concentration of electromagneticwaves can be avoided to some extent in the case of defrosting or thelike manner of heating requiring the avoidance of the concentration.However, due to the stirring caused by a constant rotation withoutregard to the kind of food, any kind of food is heated by repeating thesame electric field distribution for each rotation of the stirrer orrotary waveguide, thus making it difficult to achieve a perfectlyuniform heating distribution.

Even when a plurality of openings are formed, a certain fixed electricfield is constituted if the openings are simply opened at the same time.Accordingly, it is hard to provide a uniform heating distribution forevery kind of food. Therefore, there is actually no large difference ofthe heating distribution between the microwave oven of FIG. 1 and themicrowave oven of FIG. 3. A satisfactory cooking result cannot beexpected unless the optimum opening is switched or selected for eachindividual kind of food.

Meanwhile, in the apparatus provided with a plurality of magnetrons anda plurality of waveguides, the control of oscillation of each magnetronis followed by a switching of the waveguides and, hence, the openingthrough which the electromagnetic waves are to be emitted is switched.Although this arrangement is slightly effective to provide a uniformheating distribution, the increased number of magnetrons raises costsand makes the apparatus heavy and inconvenient to carry.

When a plurality of waveguides are branched in many directions from onewaveguide, the opening easy for the electromagnetic waves to passthrough cannot be switched perfectly, i.e., a certain amount ofelectromagnetic waves leak also from the openings not selected.Moreover, a large quantity of sheet metal is needed for the waveguides,causing the apparatus to be expensive and hard to manufacture.

As a solution to the above, end faces 14 of the sub waveguides 13 aremoved at positions facing the openings 5, as shown in FIG. 4, to therebyselect the opening 5 which apparently is easy for the electromagneticwaves to pass through. Although the heating distribution is providedmore or less effectively uniform according to this method, the space forthe plurality of sub waveguides 13 and the space for a plurality ofshields to prevent the leak of electromagnetic waves when the end faces14 of the sub waveguides 13 are moved are required in practice. As aresult, the whole microwave oven becomes bulky or the effective volumeof the heating chamber to the whole apparatus is reduced, leading tosuch a user's dissatisfaction that the apparatus occupies a considerablespace or affords to contain only small food. At the same time, theapparatus becomes heavy and hard to carry. An amount of power isprobably consumed to move the end faces 14 of the sub waveguidesincluding the shields at a plurality of positions.

As shown in FIG. 5, even if the metallic part is moved within onewaveguide 3 having a plurality of openings 5, it is impossible tocompletely switch to select the opening easy for the electromagneticwaves to pass. Unrequested openings 5 are also open, through which theelectromagnetic waves leak.

In the constitutions of FIGS. 1, 3, 4 and 5, the openings 5 are formedonly at a side face of the apparatus, in other words, separated far fromthe food 6.

If the distance between the opening 5 and the food 6 is large, the rateof the electromagnetic waves not only entering the food 6 directly fromthe opening 5, but entering the food 6 after reflected at the wall faceof the heating chamber 4, etc. is increased. In consequence of this, theheating distribution of the food 6 is disadvantageously changed large bythe size of the heating chamber 4, or the position or shape of the food6.

From the same reason as above, a peripheral portion of the general food6 tends to be heated more easily.

The arrangement of FIG. 6 or 7 is more useful to provide a uniformheating distribution than the other conventional arrangements. However,the peripheral portion of the food is still easy to heat because of theelectromagnetic waves always radiated from the upper part of the heatingchamber and, a portion of the food between one and the other openingsadjacent to each other at the lower part of the heating chamber is hardto heat.

What is common to these conventional arrangements of FIGS. 1, 3, 4, 5, 6and 7 is an undesirable probability that the electromagnetic waves willbe concentrated only where the openings 5 are formed, causing a heatingirregularity.

In the arrangements of FIGS. 3 and 5-7, the distance from the magnetron2 to the opening 5 is not taken into account.

Generally, whether or not it is easy for the electromagnetic waves toenter the heating chamber 4 is determined by matching of the heatingchamber and openings, and is changed depending on the position of theopenings 5 in the heating chamber 4, the length of the waveguide 3, thedistance between the magnetron 2 and the opening 5, etc. Particularly,the ease at which electromagnetic waves come out from the waveguide 3varies with a cycle of λg/2 wherein λ is the guide wavelength of theelectromagnetic waves. Therefore, when a plurality of openings 5 arepresent, the matching should be adjusted for each opening 5 so as toemit the electromagnetic waves equally from all the openings 5.

Unless the matching is achieved by determining the position of theopening 5 solely to lengthen the distribution it becomes, theelectromagnetic waves to enter the heating chamber, whereby the heatingefficiency is worsened. In addition, an increased amount of reflectingwaves enter the magnetron 2, which necessitates countermeasures toprevent a temperature rise or generation of unnecessary radiationnoises.

In the feedback control by detecting the state of food, an initialheating state or a state change from a heating start has been detectedor heating completion has been detected with the use of a weight sensor,a humidity sensor, a temperature sensor, an electromagnetic fielddetection sensor, a steam detection sensor, an alcohol detection sensoror the like. Any of the aforementioned sensors have not been practicallydesigned to carry out such feedback control as to detect the heatingdistribution or correct the heating irregularity.

SUMMARY OF THE INVENTION

The present invention has been devised to solve the above-describedproblems inherent in the prior art and is intended to provide a highfrequency heating apparatus which can heat an optional portion of anobject to be heated and provides a uniform heating distribution of wholeobject by a combined heating over optional portions.

Another object of the present invention is to provide a high frequencyheating apparatus which can heat an optional portion of an object to beheated and distinguish a portion to be heated and a portion not to beheated.

A further object of the present invention is to provide a high frequencyheating apparatus which can maintain or improve the heating efficiencyto enhance the reliability.

A still further object of the present invention is to provide a highfrequency heating apparatus which can automatically heat an optionalportion of an object to be heated, exactly in a manner as set.

In accomplishing the above-described objects, a high frequency apparatusaccording to the present invention comprises an electromagnetic waveemission means for emitting electromagnetic waves, a local heating meanscapable of heating an optional portion of an object to be heated by theelectromagnetic waves emitted from the electromagnetic wave emissionmeans, and a control means for controlling the local heating means.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing the constitution of a conventional highfrequency heating apparatus.

FIG. 2 is a view showing the constitution of another conventional highfrequency heating apparatus.

FIG. 3 is a view showing the constitution of a further conventional highfrequency heating apparatus.

FIG. 4 is a view showing the constitution of a yet further conventionalhigh frequency heating apparatus.

FIG. 5 is a view showing the constitution of a still furtherconventional high frequency heating apparatus.

FIG. 6 is a view of another conventional high frequency heatingapparatus.

FIG. 7 is a sectional view of an essential part of the high frequencyheating apparatus shown in FIG. 6.

FIG. 8 is a view showing the constitution of a high frequency heatingapparatus according to a first embodiment of the present invention.

FIG. 9 is a view of the constitution of an essential part of the highfrequency heating apparatus shown in FIG. 8.

FIG. 10 shows a rotary waveguide and a driving part mounted in the highfrequency heating apparatus of FIG. 8, (a) being a top plan view of therotary waveguide, (b) a longitudinal sectional view of the rotarywaveguide and the driving part, and (c) a view showing an engagementstate of a cam and a switch of the driving part.

FIG. 11 is a bottom view of the high frequency heating apparatus of FIG.8.

FIG. 12 is a view of a state when a food in a heating chamber of thehigh frequency heating apparatus of FIG. 8 is heated.

FIG. 13 is a view of a state when the food and the rotary waveguide arerotated from the state of FIG. 12.

FIG. 14 is a characteristic diagram of a heating distribution of thefood when the states of FIGS. 12 and 13 are switched.

FIG. 15 is a view of a heating state of the food when an emission portof the rotary waveguide is inclined 45° to the food.

FIG. 16 is a view of a heating state of the food when the emission portof the rotary waveguide is inclined 45° to the food and the rotation ofthe food is stopped.

FIG. 17 is a bottom view of a turntable.

FIG. 18 is a lateral sectional view of a heating chamber of a highfrequency heating apparatus according to a second embodiment of thepresent invention.

FIG. 19 shows a third embodiment of the present invention, (a) being atop plan view and (b) a longitudinal sectional view of the rotarywaveguide.

FIG. 20 shows a fourth embodiment of the present invention, (a) being atop plan view and (b) a longitudinal sectional view of a rotary antenna.

FIG. 21 shows a fifth embodiment of the present invention, (a) being atop plan view and (b) a longitudinal sectional view of a shieldingmember with an opening.

FIG. 22 shows a sixth embodiment of the present invention, (a) being alongitudinal view and (b) a horizontal sectional view of a heatingchamber of a high frequency heating apparatus.

FIG. 23 is a view showing the constitution of a high frequency heatingapparatus according to a seventh embodiment of the present invention.

FIG. 24 is a front view of an operation panel of the high frequencyheating apparatus of FIG. 23.

FIG. 25 is a horizontal sectional view of the high frequency heatingapparatus of FIG. 23 with an emission port of a rotary waveguidedirected to the center.

FIG. 26 is a horizontal sectional view of the high frequency heatingapparatus of FIG. 23 with the emission port of the rotary waveguidedirected to a wall face of a heating chamber.

FIG. 27 is a characteristic diagram indicating a relation of the heatingtime and the temperature of food in the conventional high frequencyheating apparatus.

FIG. 28 is a characteristic diagram indicating a relation of the heatingtime and the temperature of food in the high frequency heating apparatusof the present invention.

FIG. 29 is a characteristic diagram showing a timing for switching thedirection of the emission port in the high frequency heating apparatusof the present invention.

FIG. 30 is a characteristic diagram of a relation of the heating timeand the temperature of food in a high frequency heating apparatus of aneighth embodiment of the invention.

FIG. 31 is a temperature characteristic diagram of the dielectric lossof water.

FIG. 32 is a characteristic diagram of a relation between the time andthe heating output when a frozen food is defrosted with the use of theconventional high frequency heating apparatus.

FIG. 33 is a characteristic diagram of a timing for switching theheating output in FIG. 32.

FIG. 34 is a characteristic diagram of a relation between the time andthe temperature of frozen food when the food is defrosted with the useof the high frequency heating apparatus of the present invention.

FIG. 35 is a characteristic diagram of a timing for switching theheating output in FIG. 34.

FIG. 36 is a characteristic diagram of a relation between the time andheating output in FIGS. 34 and 35.

FIG. 37 is a view showing the constitution of a high frequency heatingapparatus according to a ninth embodiment of the present invention.

FIG. 38 is a sectional view taken along the line A-A' in FIG. 37.

FIG. 39 is a characteristic diagram showing a change in direction ofelectromagnetic waves subsequent to the operation of a rotary waveguidein FIG. 38.

FIG. 40 is a view of the configuration of a high frequency heatingapparatus according to a tenth embodiment of the present invention.

FIG. 41 is a horizontal sectional view of a lower part of a heatingchamber of the high frequency heating apparatus of FIG. 40.

FIG. 42 is a characteristic diagram of a change in direction ofelectromagnetic waves subsequent to the operation of a rotary waveguidein the constitution of FIGS. 40 and 41.

FIG. 43 is a longitudinal sectional view of an essential part of a highfrequency heating apparatus according to an eleventh embodiment of thepresent invention, indicating a state where a rotary waveguide is movedup.

FIG. 44 shows a state where the rotary waveguide of FIG. 43 isdescended.

FIG. 45 is a view showing the constitution of a high frequency heatingapparatus according to a twelfth embodiment of the present invention.

FIG. 46 shows two shielding plates set in the high frequency heatingapparatus of FIG. 45, (a) being a top plan view of a first shieldingplate and (b) being a top plan view of a second shielding plate.

FIG. 47 is a view showing the constitution of a high frequency heatingapparatus according to a thirteenth embodiment of the present invention.

FIG. 48 is a sectional view taken along the line B-B' in FIG. 47.

FIG. 49 is a diagram showing detection positions of an infrareddetection element set in the high frequency heating apparatus of FIG.47.

FIG. 50 is a block diagram of the high frequency heating apparatus ofFIG. 47.

FIG. 51 is a characteristic diagram of a surface temperature change offood and a temperature change of parts other than the food in the highfrequency heating apparatus of FIG. 47.

FIG. 52 is a block diagram of a modified example of FIG. 50.

FIG. 53 is a block diagram of a high frequency heating apparatusaccording to a fourteenth embodiment of the present invention.

FIG. 54 is a view showing the constitution of a high frequency heatingapparatus according to a fifteenth embodiment of the present invention.

FIG. 55 is a sectional view taken along the line F-F' in FIG. 54.

FIG. 56 is a view showing the constitution of a high frequency heatingapparatus according to a sixteenth embodiment of the present invention.

FIG. 57 is a sectional view taken along the line G-G' in FIG. 56, (a)being a view of a state when a first opening is shielded, and (b) beinga view of a state when a second opening is shielded.

FIG. 58 is a block diagram of a high frequency heating apparatusaccording to a seventeenth embodiment of the present invention.

FIG. 59 is a temperature characteristic diagram explanatory of theoperation of an outline extraction means set in the high frequencyheating apparatus of FIG. 58, (a) indicating the position of the food,(b) indicating detection positions in an X direction, (c) indicatingdetection positions in a Y direction and (d) being a synthetic view ofdetection positions in the X direction and Y direction.

FIG. 60 is a block diagram of a high frequency heating apparatusaccording to an eighteenth embodiment of the present invention.

FIG. 61 is a block diagram of a high frequency heating apparatusaccording to a nineteenth embodiment of the present invention.

FIG. 62 is a view showing the constitution of an essential part of ahigh frequency heating apparatus according to a twentieth embodiment ofthe present invention.

FIG. 63 is a longitudinal sectional view of an essential part of a highfrequency heating apparatus according to a twenty-first embodiment ofthe present invention in a state where a turntable is raised.

FIG. 64 is a state where the turntable of FIG. 63 is lowered.

FIG. 65 is a bottom view of a turntable set in a high frequency heatingapparatus according to a twenty-second embodiment of the presentinvention.

FIG. 66 is a longitudinal sectional view of an essential part of a highfrequency heating apparatus according to a twenty-third embodiment ofthe present invention.

FIG. 67 is a view showing the constitution of a high frequency heatingapparatus according to a twenty-fourth embodiment of the presentinvention.

FIG. 68 is a longitudinal view of an essential part of a high frequencyheating apparatus according to a twenty-fifth embodiment of the presentinvention, particularly showing a distribution state of electric fields.

FIG. 69 is a perspective view of an essential part of a high frequencyheating apparatus according to a twenty-sixth embodiment of the presentinvention.

FIG. 70 is a view showing the constitution of an essential part of ahigh frequency heating apparatus according to a twenty-seventhembodiment of the present invention in a state where one of two openingsis shielded, (a) being a longitudinal sectional view and (b) being a topplan view.

FIG. 71 shows a state where the other opening of FIG. 70 is shielded,(a) being a longitudinal sectional view and (b) being a top plan view.

FIG. 72 is a Rieke diagram showing working points of a magnetron in thehigh frequency heating apparatus of FIG. 70.

FIG. 73 is a characteristic diagram of a change of a high frequencyoutput in the high frequency heating apparatus, (a) showing the outputchange in the prior art and (b) showing the output change in the presentinvention.

FIG. 74 is a view of the constitution of a high frequency heatingapparatus according to a twenty-eighth embodiment of the presentinvention.

FIG. 75 is a sectional view taken along the line P-P' in FIG. 74.

FIG. 76 is a sectional view of a high frequency heating apparatusaccording to a twenty-ninth embodiment of the present invention, whichcorresponds to FIG. 75.

FIG. 77 is a sectional view of a high frequency heating apparatusaccording to a thirtieth embodiment of the present invention, whichcorresponds to FIG. 75.

FIG. 78 is a Smith chart of a heating efficiency characteristic of thehigh frequency heating apparatuses of the twenty-eighth, twenty-ninthand thirtieth embodiments, indicating a matching state of a load seenfrom a magnetron.

FIG. 79 is a view showing the constitution of a high frequency heatingapparatus according to a thirty-first embodiment of the presentinvention.

FIG. 80 is a longitudinal sectional view of an essential part of thehigh frequency heating apparatus of FIG. 79 in a state where a seal partis lowered.

FIG. 81 shows a state where the seal part of FIG. 80 is raised.

FIG. 82 is a perspective view of an essential part of a high frequencyheating apparatus according to a thirty-second embodiment of the presentinvention.

FIG. 83 is a characteristic diagram of a heating distributionirregularity when milk is heated in the high frequency heating apparatusof FIG. 82.

FIG. 84 is a schematic longitudinal sectional view of the high frequencyheating apparatus under the optimum condition of FIG. 83.

FIG. 85 is a characteristic diagram of the heating distributionirregularity when 100 g of frozen sliced beef is defrosted in the highfrequency heating apparatus of FIG. 82.

FIG. 86 is a schematic longitudinal sectional view of the high frequencyheating apparatus under the optimum condition of FIG. 85.

FIG. 87 is a characteristic diagram of the heating distributionirregularity when 300 g of frozen sliced beef is defrosted in the highfrequency heating apparatus of FIG. 82.

FIG. 88 is a schematic longitudinal sectional view of the high frequencyheating apparatus under the optimum condition of FIG. 87.

FIG. 89 is a flow chart of a sequence of procedures for determining aproper position of an opening and a proper height of food in an initialstate in the constitutions of FIGS. 79-82.

FIG. 90 is a view of a structure for simulating electric fields insidethe high frequency heating apparatus.

FIG. 91 is a perspective view taken along the line S-S' in FIG. 90showing a characteristic of a simulation result when a first openingalone is opened.

FIG. 92 is a perspective view taken along the line S-S' in FIG. 90showing a characteristic of a simulation result when a second openingalone is opened.

FIG. 93 is a perspective view of a flat food to be heated in the highfrequency heating apparatus of FIG. 90.

FIG. 94 is a perspective view taken along the line U-U' in FIG. 93showing a characteristic of a simulation result when a first openingalone is opened.

FIG. 95 is a perspective view taken along the line U-U' in FIG. 93showing a characteristic of a simulation result when a second openingalone is opened.

FIG. 96 is a longitudinal sectional view of an essential part of thehigh frequency heating apparatus for explaining the propagation ofelectromagnetic waves in a waveguide.

FIG. 97 is a view showing the constitution of a high frequency heatingapparatus according to a thirty-third embodiment of the presentinvention.

FIG. 98 is a sectional view taken along the line V-V' in FIG. 97.

FIG. 99 is a sectional view taken along the line W-W' in FIG. 97.

FIG. 100 is a characteristic diagram showing how an electric field isdeflected in the high frequency heating apparatus of FIG. 97.

FIG. 101 is a sectional view of a heating chamber for explaining howdifferently the electric fields are generated depending on the positionof the opening in the wall face of a high frequency heating apparatus.

FIG. 102 is a view similar to FIG. 101 when the position of the openingis changed.

FIG. 103 is a view similar to FIG. 101 when the position of the openingis further changed.

FIG. 104 is a view similar to FIG. 101 when the position of the openingis still further changed.

FIG. 105 is a Smith chart of a heating efficiency characteristic of ahigh frequency heating apparatus according to a thirty-fourth embodimentof the present invention, showing the matching state seen from themagnetron.

FIG. 106 is a top plan view of a plurality of shaomais placed on aplate.

FIG. 107 is a characteristic diagram of a temperature irregularity whenthe shaomais of FIG. 106 are heated in the conventional high frequencyheating apparatus.

FIG. 108 is a characteristic diagram of a temperature irregularity whenthe shaomais of FIG. 106 are heated in the high frequency heatingapparatus of the present invention.

FIG. 109 is a characteristic diagram of a temperature irregularity whenthe shaomais of FIG. 106 are heated in another high frequency heatingapparatus of the present invention.

FIG. 110 is a horizontal sectional view of a high frequency heatingapparatus according to a thirty-fifth embodiment of the presentinvention.

FIG. 111 is a Smith chart of a heating efficiency characteristic of ahigh frequency heating apparatus according to a thirty-sixth embodimentof the present invention, showing the matching state shifted at thefirst opening.

FIG. 112 is a horizontal sectional view of a high frequency heatingapparatus according to a thirty-seventh embodiment of the presentinvention.

FIG. 113 is a sectional view taken along the line Y-Y' in FIG. 112.

DETAILED DESCRIPTIONS OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described belowwith reference to the drawings.

FIG. 8 is a sectional view showing the constitution of a high frequencyheating apparatus according to a first embodiment of the presentinvention.

Electromagnetic waves emitted from a magnetron 2, which is arepresentative emission means for emitting electromagnetic waves, areradiated to a heating chamber 4 via a waveguide 3 as a waveguide partand a power feed chamber 15, so that a food 6 as an object to be heatedmay be heated in the heating chamber 4. The electromagnetic waves in thewaveguide 3 heat an optional local portion of the food 6 by means of arotary waveguide 8 as an emission part arranged in the power feedchamber 15. The waveguide 3 and rotary waveguide 8 will be namedtogether as a local heating means 16 herein. The rotary waveguide 8 hasa directivity in an emission direction of the electro-magnetic waves,switching the emission direction through the rotation thereof to therebyrealize local heating. For this purpose, the rotary waveguide 8 isprovided with a coupling part 7 which is coupled with the waveguide 3 totake out the electromagnetic waves, and arranged astride the waveguide 3and the power feed chamber 15 (heating chamber 4 when the power feedchamber 15 is not provided). An emission port 17 is formed in the rotarywaveguide 8 through which the electromagnetic waves taken out from thewaveguide 3 are emitted.

The coupling part 7 is connected to a motor 18 as a driving means andcan be rotated by the motor 18 and, the rotary waveguide 8 itself isrotated about the coupling part 7. A control means 19 controls the motor18, so that the direction of the electromagnetic waves can be controlledby the emission port 17 of the rotary waveguide 8, thereby providingcontrol of the local heating.

The food 6 is placed on a stage 20 for subsequent heating of an optionalportion thereof. The stage 20 is set on a glass or ceramic saucer 21 asa wave transmission part constructed on the turntable 1 having a waveshielding metallic part. The stage 20 together with the saucer 21 isrotated by a motor 22 as a stage driving means. At this time,simultaneously with the rotation of the motor 22, the control means 19performs control in accordance with the weight of the food 6 detected bya weight sensor 23 (control to estimate a driving timing of the rotarywaveguide 8, a heating output or a heating end time, etc.). A rotationalcenter of the stage 20 at this moment is at a center 24 of a bottom faceof the heating chamber 4. Heating in a rotational direction is madeuniform by the constant rotation of the stage 20 or local heating iscarried out by stopping and decelerating the stage 20 at a predeterminedposition. On the other hand, a rotational center of the rotary waveguide8 is shifted from the center 24 of the bottom face of the heatingchamber 4. The emission direction of electromagnetic waves to the food 6is changed by the direction of the emission port 17, making it possibleto switch heating of the center of the food 6 or the periphery of thefood 6. In other words, the heating position is changeable in a radialdirection of the stage 20, and accordingly, an optional position on thestage 20 can be heated in association with the rotation of the turntable1.

Due to the arrangement that the rotational center of the stage 20 is atthe center 24 of the bottom face of the heating chamber 4, the stage 20can be formed large or the food 6 may be large-sized and increased innumber.

Since a center of the stage 20 agrees with the rotational centerthereof, a stage face is controlled not to move up and down during therotation, and therefore a target position of the food 6 is locallyheated with ease. Besides, the food 6 is hard to vibrate and spill.

In a general microwave oven, an opening is often covered with a cover ofa low dielectric loss hard to absorb electromagnetic waves from the sideof the heating chamber 4. In this embodiment, a cover 25 as a protectingmeans for the local heating means 16 is provided so as to cover thepower feed chamber 15, to thereby reduce a level difference or heightdifference to the bottom face of the heating chamber 4.

The above cover 25 in this embodiment is different from the conventionalopening cover, which will be described more in detail.

The conventional opening cover has been intended primarily to prevent auser from erroneously putting fingers inside or prevent dust fromaccumulating in the opening. In contrast, according to this embodiment,since the rotary waveguide 8 should be controlled as required in orderto locally heat the food, the cover 25 is arranged so as to prevent thescum of the food 6 from scattering to directly hit and stop the rotarywaveguide 8, or accumulating in the vicinity of the rotary waveguide 8and absorbing the electromagnetic waves whereby a target portion of thefood cannot be heated. That is, the cover 25 is effective to ensure thelocal heating by the local heating means 16.

The control means 19 performs control other than the above, e.g.,monitors a temperature change of the food 6 by a temperature sensor 26which detects a temperature distribution of the food 6, or controls theemission of electromagnetic waves from the magnetron 2, the operation ofa fan 27 for cooling the magnetron 2 or the operation of a heater 28.

Generally, the interior of the heating chamber 4 rises to 300° C. or sowhen the heater 28 is used. The glass saucer 21 is sometimes replacedwith a metallic one because of limited heat-proof temperatures of glass.A ceramic saucer with high heat-proof temperatures is shared in somecases to eliminate the trouble in exchanging the saucer 21 depending onwhether the heating is done by electromagnetic waves or by the heater.

The temperature sensor 26 detects the temperature of the food 6 throughan opening 29 at a wall face of the heating chamber 4, thereby detectinga heating distribution. The constitution of the temperature sensor 26will be additionally depicted here. As an example of the generaltemperature sensor 26 for detecting the temperature in a non-contactmanner, there is an infrared sensor converting the amount of infraredrays emitted from the food 6 to electric signals. The infrared sensorincludes a thermopile sensor internally provided with a hot contact anda cold contact, a pyroelectric sensor provided with a chopper, etc. anyof which will do in the present invention.

FIG. 9 is a view of an essential part showing a positional relation ofthe magnetron 2 and the rotary waveguide 8.

The distance l1 for the electromagnetic waves emitted from an antenna 30of the magnetron 2 and run to reach the coupling part 7 of the rotarywaveguide 8 is set to be approximately an integral multiple of λg/2 whenλg is a guide wavelength in the waveguide 3, because the electromagneticwaves in the waveguide 3 are standing waves repeatedly and periodicallyturned intense and weak, a wavelength of which agrees with λg. Anelectric field at the antenna 30 of the magnetron 2 is intense at alltimes. In the dimensional relation as above, the coupling part 7 of therotary waveguide 8 always has an intense electric field, so that theelectromagnetic waves in the waveguide 3 can be efficiently guidedoutside the waveguide 3.

If the distance from the antenna 30 of the magnetron 2 to an end part 31of the waveguide 3, or the distance from the coupling part 7 to an endpart 32 of the waveguide 3, is set to be approximately an odd multipleof λg/4 (one multiple in the drawing), more stable standing waves aregenerated in the waveguide 3 because an end face of the waveguide islocated right where the electric field changes from intense to weak at aposition of the odd multiple of λg/4.

According to this embodiment, even when the rotary waveguide 8 rotates,the distance from the antenna 30 of the magnetron 2 to the coupling part7 is constant, and consequently stable standing waves are effectivelyobtained.

The electric waves guided out from the coupling part 7 are radiated tothe heating chamber 4 through the emission port 17. Since the length l2is a factor determining the directivity, the length may be suitablychanged upon necessities. If the length ψ2 is an integral multiple ofλg/2, the electric field at the emission port 17 can be intense, which,from the expression (1), exerts considerably high efficiency when thefood 6 is placed close to the emission port 17.

In the drawing, l3>>l4 is held to facilitate the propagation ofelectromagnetic waves to the side of l3. Moreover, the length ψ5 is setto be nearly an odd multiple of λg/4 to further facilitate thepropagation of electro-magnetic waves towards l3.

The emission direction of electromagnetic waves is controlled in theabove constitution.

Because of the constant distance between the antenna 30 of the magnetron2 and the emission port 17 at all times, an impedance therebetween isalso kept constant at all times, so that a matching state is easy tomaintain and a heating efficiency is effectively kept high.

FIG. 10 is a view of the constitution of an essential part of the rotarywaveguide 8.

(a) is a view seen from above and (b) is a sectional view seen fromsideways. In (a), the length l6 is set to satisfy

    l6>λ.sub.0 /2

wherein λ₀ is the wavelength of the electromagnetic waves in vacuum (orin the air) and λ₀ /2 is approximately 61 mm at a frequency of 2.45 GHz,thus achieving the sure emission of the electromagnetic waves. Actually,the length l6 is preferably 65 mm or larger to leave leeway.

The rotary waveguide 8 is supported at three points, namely, two Teflonspacers 33 and a fitting part 35 formed in a shaft 34 of the motor 18,and can accordingly rotate stably.

The spacer 33 has a downward curved face and is easy to slide. Anynon-conductive material is usable for the spacer 33 so long as itensures effective support and smooth rotation to the spacer 33. Even ifthe spacer 33 is made of conductive material, an arrangement that avoidsa spark between the spacer and a bottom part 36 will serve the purpose(for instance, by holding the spacer always in tight contact with thebottom part 36 in a manner not to generate a gap therebetween).

(c) shows a cam 37 connected to the shaft 34 and a switch 38 as aposition detection means. While the rotary waveguide 8 is rotated by themotor 18, a projecting part 39 of the cam 37 presses a button 40 of theswitch 38 every one rotation of the shaft 34. Therefore, the rotationalposition of the rotary waveguide 8 is detected from a driving time sincethe button 40 is pressed, and consequently the emission direction of theelectromagnetic waves is detected and controlled as required. Thecontrol means 19 determines a rotating time of the motor 18 and controlsthe emission direction from the emission port 17 based on signals fromthe switch 38. Needless to say, if the motor 18 is required to be morecorrectly controlled in position or in rotating speed, a stepping motoror the like may be employed.

A reference position may be set to control the motor 18 so that themotor is moved to the reference position at the start or end of heating.

If the motor is controlled at the heating start time, a target portionof the food can be heated accurately. On the other hand, if the motor iscontrolled at the completion of heating, it eliminates the trouble toconfirm the reference position for a next heating.

FIG. 11 is a view showing the constitution of an essential part of thehigh frequency heating apparatus of the first embodiment, morespecifically, the bottom face of the heating chamber 4 of FIG. 8 seenfrom below. Heaters 28A, 28B and 28C are disposed in a vacant space tocoexist with the power feed chamber 15 and weight sensor 23.

For the above configuration, the rotary waveguide 8 is preferably madesmall in size. That is, the rotary waveguide 8 should be compact andhighly directive.

FIGS. 12 and 13 are sectional views of FIG. 8 seen from above the food6. In order to show the directivity of the rotary waveguide 8, a heatedportion 41 is indicated in FIGS. 12 and 13 which is obtained after thefood 6, which is a flat parallelepiped, is heated with a constantheating output while rotated at a constant speed together with thesaucer 21 although the rotary waveguide 8 is stopped at a position ofthe drawings. Parts actually unseen and hidden by the saucer 21 are alsoillustrated in the drawings by a solid line for easy understanding. Theemission port 17 is directed to the center of the saucer 21 in FIG. 12,while the emission port 17 is rotated 180° from FIG. 12 and directedoutward in FIG. 13.

In FIG. 12, the heated portion 41 appears approximately at the center ofthe food 6 subsequent to the emission of electromagnetic waves 42 frombelow.

In FIG. 13, the electromagnetic waves 42 enter the food 6 after beingreflected at wall faces of the heating chamber 4 and therefore theheated portion 41 is at edges (periphery) of the food 6. Most ofconventional microwave ovens show a similar result to FIG. 13 becausethe electromagnetic waves are reflected at wall faces of the heatingchamber before entering the food.

FIG. 14 shows the heating distribution of the food 6 resulting fromswitching of states of FIGS. 12 and 13 (switching of the direction ofthe emission port 17 with a suitable rate). The heated portion 41 isgenerated at the center and in the periphery of the food 6. In otherwords, the food 6 is considerably uniformly heated in comparison withthe case of the conventional microwave oven. An unheated portion 43which is hard to heat is left at a middle area between the center andperiphery of the food 6. This unheated portion 43 is heated by localheating in a manner as will be described below.

FIGS. 15 and 16 are sectional views of the essential part of the highfrequency heating apparatus in the embodiment, namely, sectional viewsof FIG. 8, similar to FIGS. 12 and 13. In order to heat theaforementioned unheated portion 43 at the middle area in FIG. 14, as iseasily conceived, the emission port 17 should be directed to between thecenter (0°) and outside (180°) of the saucer 21. Experiments have shown,however, that this idea bears no satisfactory result when the turntableis rotated at a constant speed. Even if the direction of the emissionport is changed a little every time, what is heated is the periphery ofthe food in most cases unless the emission is concentrated to the centerof the food. For example, when the emission port 17 assumes 45°, theresult is as shown in FIG. 15, because the saucer 21 is rotated at aconstant speed and the heating output is constant. The edges of the food6 are eventually heated except at a moment when, if it happens, themiddle area of the food can be heated during the rotation, and inconsequence, the periphery of the food is heated on the average in onecycle. A state where the middle area can be heated should be maintainedand the other state should be avoided in order to heat the middle area.

FIG. 16 results from the continued state where the middle area can beheated with the rotation of the saucer 21 stopped. The emission port 17has an angle of 45° and the food 6 is stopped at a position of thedrawing, and one of the unheated portion 43 hard to heat in FIG. 14 isheated. The food 6 should be moved another 180° to heat the otherunheated portion 43. That is, in order to uniformly heat the total food6, four kinds of operations are required, i.e., three operations inFIGS. 12, 13, 16 and one operation after moving the food 6 by 180° fromFIG. 16. The saucer 21 is allowed not to be completely stopped in themiddle of the heating or may be decelerated nearly when the middle areacan be heated.

The heating output in a state where the middle area can be heated whilethe saucer 21 is rotated at a constant speed may be set higher than inother states. In practice, the heating output in the state where themiddle area can be heated is made a full power and that in other statesis set to be 0 or reduced.

The rotation of the saucer 21 may be combined with the control of theheating output.

From the above, three elements, namely, the rotary waveguide 8, thesaucer 21 and the magnetron 2 should be controlled in association witheach other to locally heat an optional portion of the food.

FIG. 17 shows the constitution of an essential part, specifically, theturntable 1 of the high frequency heating apparatus of the embodiment,seen from below. The turntable 1 consists of rings 44, 45, shafts 46, 47and a bearing 48 and is formed of metal to stand the heat of heaters28A, 28B, 28C. Lengths l7, l8 of a crevice or opening in a rotationaldirection of the turntable 1 are not smaller than 1/2 a wavelength ofelectromagnetic waves to allow the electromagnetic waves to pass througheasily.

Although it depends on the directivity of the rotary waveguide 8, theopening in the vicinity of the center of the bottom face of theturntable as indicated by l8 in FIG. 17 is necessary to heat a centralbottom face of the food, and the opening in the periphery of theturntable as represented by l7 is necessary to heat the periphery of thefood. It is apparent, though, that the opening is not required if theturntable 1 is made of a material such as ceramic or the like which ishard to absorb electromagnetic waves and having a permeability to theelectromagnetic waves.

Accordingly, the turntable 1 should be formed of a material resistant tolower heaters 28A, 28B, 28C, or an electromagnetic wave-permeablematerial may be selected if a heater not raising a temperature at thebottom face of the turntable (a heater of a type circulating hot wind)is used, in place of the lower heaters 28A, 28B, 28C.

FIG. 18 shows a second embodiment of the present invention.

Since the rotary waveguide 8 is installed at a corner of the heatingchamber 4 according to the second embodiment, the rotary waveguide 8 canbe slightly larger in size, in other words, a degree of freedom ofdesign is increased.

A driving range of the emission port 17 is set only inside the bottomface of the heating chamber 4 as indicated in the drawing. If theemission port 17 were adapted to work outside the bottom face of theheating chamber 4, the high frequency heating apparatus would becomebulky and require special arrangements not to leak the electromagneticwaves outside. The second embodiment is constituted as above to avoidthese problems.

FIG. 19 is a high frequency heating apparatus according to a thirdembodiment of the present invention, wherein the rotary waveguide 8 ischanged in shape, with exerting the same effect. In FIG. 19(a), endfaces in all four directions of the rotary waveguide 8 are bent to becircular, thus increasingly efficiently preventing sparks. Theelectromagnetic waves are emitted through an opening 49.

In comparison with the first embodiment, the electromagnetic waves tendto be emitted immediately upward from the opening 49.

An internal space 50 can be regarded as a waveguide.

Lengths l5 between the coupling part 7 and the end face of the rotarywaveguide and, l9+l10 are respectively about an odd multiple of λg/4, sothat the standing waves are generated stably.

If the length l9 is set to be approximately an odd multiple of λg/4 andthe length l10 is set to be approximately an integral multiple of λg/2,this is effective to generate standing waves more stably.

The above will be explained with reference to FIG. 19(b) showing howelectric fields are generated at a moment. The electric field ispractically repeatedly reversed with a cycle of an inverse number of afrequency. An arrow-headed solid line 51a indicates a direction ofrepresentative electric fields having three ridges of standing waves(field loops) generated in the internal space 50. Electric fieldsindicated by an arrow-headed solid line 51b are generated in thevicinity of the opening 49, and consequently strong electric fields 51cholding the opening 49 therebetween are induced above the opening 49.

The generation of these electric fields 51a and, 51b and 51c takes placeconcurrently because of the above-described dimensional relationship,and accordingly the electromagnetic waves are emitted from the opening49 without disturbing the standing waves.

FIG. 20 shows a fourth embodiment, in which a rotary antenna is employedin place of the rotary waveguide.

A conductive sheet body 53 (specifically, iron or stainless sheet body)connected to the coupling part 7 has a directivity, exerting the sameeffect as discussed hereinabove.

FIG. 21 shows a fifth embodiment. A position where the opening is shutis switched in the constitution of the fifth embodiment.

An opening 55 is formed in an electrically conductive sheet body 54connected to the coupling part 7, while other parts than the opening 55are shielded.

The opening 55 accordingly shows a directivity thereby to achieve thesame effect. The same effect is expectable in other designs so long asthe directivity is secured. The fourth and fifth embodiments are hard toattain the aimed directivity in comparison with the first-thirdembodiments, while the structure itself becomes simple in the fourth andfifth embodiments without requiring bending, etc.

FIG. 22 shows a sixth embodiment of the present invention.

The stage 20 is constituted of the glass saucer 21 and a roller ring 56.A recess 57 is formed in the saucer 20, in which a shaft 58 of anotherpart is fitted. The stage 20 is rotated while held by the roller ring56.

(a) is a sectional view and (b) shows the constitution of the rollerring 56 seen from above.

The roller ring 56 has a ring 59 and three rollers 60. The ring androllers are formed of a material passing electromagnetic waves.

In the above constitution, the electromagnetic waves emitted from therotary waveguide 8 enter the food 6 without being interrupted.

A target local portion of the food is heated easily. Although not shownin the drawing, the bottom face of the heating chamber 4 is recessed soas to let the rollers 60 smoothly move without a positional shift.

A seventh embodiment of the present invention is shown in FIGS. 23-29.The rotary waveguide 8 projects into the heating chamber 4 in FIG. 23.In this case, the cover 25 is formed like a box to protect the rotarywaveguide 8.

The constitution of the embodiment effectively reduces the occupiedspace below the bottom face of the heating chamber 4, whereas theeffective volume of the heating chamber 4 is disadvantageouslydecreased.

Photosensors 61, 62 as shape detection means are installed in thepresent embodiment, so that a shape of the food 6 can be detected fromwhether the light from the light emitting part 61 is received at thephotodetecting part 62.

In the case where the food 6 has the same temperature as the saucer 21,the temperature sensor 26 cannot instantaneously detect an area wherethe food 6 is present. However, data obtained by the photosensors 61, 62and weight sensor 23 make it possible to determine the area where thefood 6 is present before the food 6 is heated.

Since only the area where the food 6 exists can be locally heated,heating of parts other than the food 6 is prevented, thus eliminatingwaste and improving the heating efficiency.

A setting means 63, allowing the user to set the apparatus manually, isprovided in the embodiment.

Although portions to be locally heated can be determined simply by theinput contents in some cases, the direction of the rotary waveguide 8,the rotation of the turntable 1, the output of the magnetron 2, etc. arecontrolled in most cases based on the judgment by an area judging andcontrolling means (not shown) of the control means 19 along with theinput contents and data of the temperature sensor 26, photosensors 61,62 and weight sensor 23.

FIG. 24 indicates the constitution of an essential part of the highfrequency heating apparatus of the embodiment, namely, an operationpanel 64 as the setting means 63 referred to above.

In warming milk, the user presses a milk key 65 after bringing the milkin the heating chamber 4 and presses a start key 66. The control means19 judges that the food 6 is milk based on a signal from the operationpanel 64, and detects the amount, shape, location and initialtemperature of the milk from signals from the weight sensor 23,photosensors 61, 62 and temperature sensor 26, thereby determining aproper position of the emission port 17. The control means 19 furthercalculates how much the motor should be moved from the referenceposition, then driving the motor 18 to start the emission ofelectromagnetic waves from the magnetron 2.

At this time, if the milk is placed near the emission part, theturntable 1 is stopped and the rotary waveguide 8 is moved to heatimmediately below the milk.

If the milk is far from the emission port 17 (e.g., at the opposite sidevia a shaft 67 of the motor 22), both the turntable 1 and the rotarywaveguide 8 are controlled into such a positional relationship that canheat immediately below the milk.

On the other hand, if the milk is set at the center of the turntable 1,there is no large difference whether the turntable 1 is moved orstopped. If the rotary waveguide 8 is controlled to direct theelectromagnetic waves to the center as shown in FIG. 25, the milk isnaturally heated immediately therebelow.

When a plurality of cups or bottles of milk are placed in the heatingchamber, the turntable 1 and the rotary waveguide 8 are both moved tosequentially heat immediately below the plurality of cups or bottles ofmilk.

In the case of milk, if the electric fields are concentrated at thebottom face, not only is the heat is naturally distributed well owing tothe convection, but the matching state is favorable, whereby the heatingefficiency is improved.

When it results the same whether the turntable is moved or not, it isbetter not to move the turntable so as to save energy.

The heating of milk is continued for a time determined by the weightsensor 23 and photosensors 61, 62, or the heating is terminated when thetemperature sensor 26 judges that the milk is raised to a propertemperature.

If the turntable 1 or rotary waveguide 8 are repeatedly driven andstopped many times, the operation of the apparatus may become instablebecause the impedance seen from the magnetron 2 is changed at thedriving time of the turntable or rotary waveguide. Therefore, theoscillation of the magnetron 2 is stopped or the heating output of themagnetron 2 is decreased before the turntable or rotary waveguide isstarted. In contrast, after the turntable 1 or rotary waveguide 8 isstopped, the magnetron 2 is oscillated to increase the output. Theoperating state of the magnetron 2 is stabilized in this manner, andunnecessary radiation noises from the magnetron 2 are suppressed.

Incidentally, when a small solid food such as potatoes or the like is tobe heated, if the electromagnetic waves are emitted only from below thefood, a lower portion of the food is heated too much due to the absenceof convection. For solving this problem, the electromagnetic waves areemitted in a direction where the food 6 is not present, as shown in FIG.26. In other words, the local heating is avoided and the food is heatedby the electromagnetic waves reflected at the wall faces of the heatingchamber 4.

Now, it will be described how many shaomais or a flat food 6 such as apizza is heated.

FIG. 27 is a characteristic diagram when the conventional microwave ovenis normally used, in which an axis of abscissa indicates a heating timet and an axis of ordinate indicates a temperature T of the food 6.

An average temperature Tout at a peripheral portion of the food 6 and anaverage temperature Tin at a central portion of the food 6 are notprecise values. A target average temperature Tref when the heating iscompleted is set to be 80° C. When the heating is started, Tout quicklyincreases while Tin is hard to raise. Tout becomes Tref after theheating for t1 and reaches a saturation temperature (boilingtemperature) in t2. If the heating is stopped at this time point, Tin istoo low. Under the circumstances, the heating is continued for t3 toraise Tin to an acceptable value, when the heating is terminated. Inthis case, the peripheral portion of the food 6 is heated too much(Tout>Tref), but the central portion is not sufficiently heated(Tin<Tref). The food is cooked miserably.

On the other hand, FIG. 28 is a characteristic diagram of theembodiment. The effect of the uniformed heating by changing thedirection of the emission port 17 once in the middle of heating isconfirmed from FIG. 28. At the start of the heating, the emission port17 is directed the same as in FIG. 12 or FIG. 25 to heat the centralportion of the food 6 first. When it is t4, the emission port 17 isrotated 180° into the same direction as in FIG. 13 or FIG. 26.Therefore, Tin rises quickly until t4 while Tout does not rise smoothly.The temperature rise rate is reversed after t4, that is, Tout rises morequickly than Tin. When the heating is stopped at t5, the peripheralportion and the central portion of the food are properly heated(Tout≈Tin≈Tref) in a very good state. Since an overheated portion is notgenerated in this way of heating, a heating loss is little and theheating is finished in a short time (t5<t3).

FIG. 29 is a characteristic diagram explanatory of how to determine aswitching timing for the direction of the emission port 17 in FIG. 28.An axis of abscissa is a weight m of the food 6 detected by the weightsensor 23 and an axis of ordinate is the time t. The heavier the food 6is, the longer an optimum heating time becomes. Therefore, the switchingtime t4 of the emission port 17 can be calculated as a function of m inthe control means 19. Needless to say, the heating end time t5 can bealso determined in the same manner.

Other switching methods may be used as well. For example, in an eighthembodiment of the present invention shown in FIG. 30, the switchingtiming for the emission port 17 is feedback-controlled by thetemperature of the food 6. The method of FIG. 30 is slightly differentfrom FIG. 28. The temperature of the food 6 is monitored by thetemperature sensor 26 in real time, and the emission port 17 is switchedwhen Tin reaches Tk (Tk is a value determined in the control means 19and lower than Tref). The temperature is continuously monitoredthereafter. The heating is finished at t6 when the food 6 truly becomesTref. The temperature sensor 26 actually measures the temperature of thefood 6 and therefore the method of FIG. 30 is more accurate as comparedwith when the temperature is estimated from the weight m.

The above switching is not necessarily limited to one time, and theswitching by several times is rather preferred to avoid an increase ofthe temperature difference. When the temperature of the food is actuallymeasured and if a low temperature portion is detected in the food, it issuitable to locally heat the low temperature portion instantly.

In order to uniformly heat any food 6 at all times withoutirregularities in the heating distribution, data of the switching timingfor the emission port 17 along with the optimum direction of theemission port in combination with the rotation of the turntable 1 andthe oscillation of the magnetron 2, etc. may be stored beforehand as adatabase in a microcomputer of the control means 19 for every conditionsuch as the material, shape, location, temperature and the like of thefood 6. The present embodiment adopting this idea realizes the controlfor the optimum heating by comparing, by means of the control means 19,the input contents through the operation panel 64 and outputs from thetemperature sensor 26, weight sensor 23 and photosensors 61, 62 with thedatabase.

FIGS. 31-36 are characteristic diagrams when the food 6 in a frozenstate (-20° C.) is defrosted.

Referring first to FIG. 31, a temperature characteristic of a dielectricloss εr-tan δ of water is shown. An axis of abscissa is a temperature Tof water and an axis of ordinate is the dielectric loss εr-tan δ ofwater. The water in a frozen state (not higher than 0° C.) has a smalldielectric loss and the melted water (not lower than 0° C.) shows anextraordinarily large dielectric loss (the dielectric loss is suddenlyincreased to approximately 1000 times). In the meantime, the electricityabsorbed per unit volume by electromagnetic waves is proportional to thedielectric loss εr.tan δ as expressed by the equation (1). Therefore, itis considerably easy for the melted portion of the food is to absorb theelectromagnetic waves, causing an increased temperature difference inthe food in accordance with the progress of the heating. That is, theheating by electromagnetic waves, if continued with the same heatingdistribution as when the food is partially melted, always brings aboutthe temperature irregularity.

The need for sensitive control is brought about.

When a frozen meat or fish is to be defrosted, after the food 6 is putin the heating chamber 4, a defrost key 68 shown in FIG. 24 isdepressed, followed by the start key 66. The control means 19 judgesthat the food 6 is frozen from the signal of the operation panel 64, anddetects various kinds of data of the food such as the amount, shape, setposition, initial temperature, etc. from signals of the weight sensor 23and photosensors 61, 62, thereby determining a suitable rotating numberof the rotary waveguide 8. The motor 18 is consequently driven and themagnetron 2 is started to emit the electromagnetic waves almostsimultaneously. At this time, the turntable 1 is rotated along with therotary waveguide 8 to avoid the partial concentration of electric fieldsas much as possible.

If the temperature difference mentioned above starts to be generated,the rotary waveguide 8 is repeatedly controlled in such a manner, e.g.,as to direct and stop the emission port 17 to face to thelow-temperature portion of the food to locally heat the low-temperatureportion. Although not shown here, the control means 19 includes acontinuous control means for continuously rotating the motor, anintermittent control means for intermittently driving the motor, and aswitch control means for switching the continuous control means and theintermittent control means. Therefore, the rotary waveguide 8 can becontrolled easily.

Meanwhile, the temperature suddenly rises once a part of the foodexceeds 0° C., which is unlikely to be coped with even by uniformheating to the low-temperature portion.

As a countermeasure to this inconvenience, the rotary waveguide 8 iscontrolled in association with the controlling of the output of themagnetron 2, an example of which will be depicted below.

FIGS. 32 and 33 are characteristic diagrams of the conventionalmicrowave oven.

FIG. 32 is a characteristic diagram of a change of the heating output bythe magnetron 2 when the frozen food 6 is defrosted, in which an axis ofabscissa shows the time t and an axis of ordinate is an output P. A highoutput is continuously generated for t7 at the initial stage of heating.The output is lowered for a succeeding time t8 and moreover, theintermittent heating is carried out. A ratio of stops and continuationsof heating in the intermittent heating is changed for a last time t9 todecrease an average output. In short, the output is gradually decreasedin FIG. 32. Since the temperature rise subsequent to the heating by theelectromagnetic waves is reduced by lowering the output, and a ratio ofthe temperature rise due to the thermal transmission inside the food 6and a temperature difference between the food 6 and an ambience in theheating chamber 4 is increased, the temperature irregularity is improveda little.

FIG. 33 is a characteristic diagram explanatory of how to determinet7-t9 of FIG. 32, in which an axis of abscissa indicates the weight mand an axis of ordinate indicates the time t. The switching timing forthe output from the magnetron 2 is determined only by m detected by theweight sensor 23 irrespective of how the food 6 is stored before beingheated. For example, if the stored temperature of the food beforeheating is a little high, a part of the food is possibly melted andboiled before t7. In practice, therefore, the switching timing should becorrected based on the output of the temperature sensor 26.Nevertheless, since the heating with the constant heating distributionis kept unchanged even by the above correction, the temperatureirregularity cannot be solved perfectly.

FIGS. 34-36 are characteristic diagrams of the high frequency heatingapparatus of the embodiment.

FIG. 34 is a temperature characteristic diagram when the emission port17 is stopped at a position to heat the low-temperature portion of thefood 6 to be defrosted after the rotary waveguide 8 is rotatedconstantly by the continuous control means which is switched halfway tothe intermittent control means by the switch control means. An axis ofabscissa indicates the time t and an axis of ordinate indicates thetemperature T. In the first place, the rotary waveguide 8 and theturntable 1 are respectively rotated at a constant speed thereby tostart heating. The set temperature Tk referred in FIG. 30 is set to be0° C. The heating is stopped at t10 when a temperature of ahigh-temperature portion THI reaches Tk. At the same time, the emissionport 17 and the turntable 1 are stopped in a state to heat thelow-temperature portion or decelerated in a state close to the abovestate. The electromagnetic waves are not emitted for ts afterwards orgreatly reduced to wait until a temperature of the low-temperatureportion TLow is raised to an extent. The heating output is increasedagain after t11.

The heated portion is the low-temperature portion by the emission port17 and the turntable 1 in this case, and TLow rises faster to catch upwith THI. The heating is stopped at t12 when THI≈TLow≈Tref. Due to theeffects in this way of heating that the temperature is averaged in thewait time ts and the heating distribution is switched, the food isdefrosted considerably well without generating a distributionirregularity.

FIG. 35 is a characteristic diagram explanatory of how to determine tsor t11 and t12 in FIG. 34, an axis of abscissa indicating the weight mand an axis of ordinate showing the time t. In FIG. 35, ts, t11 and t12are determined as a function of the weight m of the food 6 detected bythe weight sensor 23. It is needless to say, however, that the factorsts, t11 and t12 may be determined by correcting with the output of thetemperature sensor 26, which more accurately uniforms the heating.

FIG. 36 is a characteristic diagram of a change of the heating output ofthe magnetron 2 when defrosting the frozen food 6 in FIGS. 34 and 35,wherein an axis of abscissa represents the time t and an axis ofordinate indicates the output P. The heating is carried out continuouslywith a high output for t10 during the initial stage, then the output issuspended for ts. Finally the output is decreased until t12 while theheating is switched to intermittent heating to lower the average output.

In the embodiment, the rotary waveguide 8 is driven when the heating bythe electromagnetic waves is stopped or greatly reduced. In comparisonwith the case where the electromagnetic waves are stirred by the stirreror rotary waveguide always in the constant rotation as in the prior art,the embodiment is effective to restrict the unnecessary radiation ortemperature rise of the magnetron 2.

Further, when the emission of the electromagnetic waves from themagnetron 2 is instable, for instance, immediately after the magnetron 2is turned ON or while the rotary waveguide 8 is being switched, outputsof various sensors are adapted not to be taken in so as to avoid theinfluences by high frequency noises. More accurate control can hence beexpected.

The locally heated portion is controllable in accordance with operationsin the control means 19 based on the input set by the user or outputs ofvarious sensors.

For example, the switching timing for the local heated portion may bedetermined by the maximum temperature for every menu, a differencebetween the maximum and minimum temperatures or respective change ratesof the temperatures to a time, etc.

Meanwhile, a greater amount of thought should be taken into account whena plurality of foods 6 are to be cooked simultaneously.

If a food to be heated and a food not to be heated such as freshvegetables mingle, only the food to be heated should be subjected tolocal heating.

For such local heating as above, which zone is to be heated may be setby determining where to place the food. Alternatively, if the apparatushas a sensor to detect the nature of the food or how to cook the food,the heating zone can be automatically decided.

FIGS. 37-39 relate to a 9th embodiment of the present invention. Theapparatus of the 9th embodiment has no turntable, but has a fixed stage20 and controls the rotary waveguide 8 in two dimensions.

The rotary waveguide 8 is driven by the motor 18 to revolve on its axisas well as around an axis of the apparatus. Specifically, a gear 70interlocking with a first rotary shaft 69 of the motor 18 applies arotational force to a gear 71 with a gear ratio of 1:1, whereby a secondrotary shaft 72 is rotated, thus letting the rotary waveguide 8 rotateat the same rotating speed as the motor 18. A gear 73 rotatinginterlockingly with the first rotary shaft 69 impresses the rotationalforce to a gear 75 via a gear 74 with a gear ratio of 1:10, so that thesecond rotary shaft 72 itself rotates around the first rotary shaft 69to revolve the rotary waveguide 8 around the axis of the apparatus at1/10 the rotating speed of the motor 18. Accordingly, the rotarywaveguide 8 rotates 10 times on its own axis in one revolution aroundthe axis of the apparatus.

The cam 37 rotating interlockingly with the first rotary shaft 69 isadapted to depress the switch 38 once in one cycle so as to change thedirection of electromagnetic waves 42 to control the heated portion. Thepressed number of times of the switch 38 or the driving time after theswitch 38 is depressed determines the position of the emission port 17thereby to control the emission direction of electromagnetic waves. If astepping motor is used as the motor 18, the emission direction is morecorrectly position-controlled by the number of driving pulses after theswitch 38 is depressed. In this case, the direction of electromagneticwaves is set or detected by the cam 37 and switch 38.

The operation panel 64 is equipped with a first operation key 76 forsetting the kind of the food 6, size of the heating output, heatingtime, heating manner, etc. and a second operation key, namely, start key66 for starting heating.

The control means 19 drives the motor 18 in response to an input throughthe first operation key 76 thereby to control the rotary waveguide 8 ata proper position based on an output of the switch 38. When the startkey 66 is manipulated, the electromagnetic waves are emitted from themagnetron 2. As the heating proceeds, the control means 19 drives themotor 18 if necessary on the basis of the input contents through thefirst operation key 76 or data of the heating distribution of the food 6from the temperature sensor 26 to control the emission direction ofelectromagnetic waves from the emission port 17 or change the output ofthe magnetron 2 so as to eliminate heating irregularities.

In the embodiment, the stage 20 on which the food 6 is loaded works alsoas a protection covering the rotary waveguide 8, and therefore the stage20 is a partition plate formed of a dielectric material of a lowdielectric loss which is hard to absorb electromagnetic waves.

FIG. 38 is a sectional view taken along the line A-A' in FIG. 37. Anotch 77 where the coupling part 7 of the rotary waveguide 8 can move isformed on the bottom face of the heating chamber 4 and a notch 78 wherethe second rotary shaft 72 can move is formed on the bottom face of thewaveguide 3. The motor 18 reverses at either end face 79, 80 of thenotches. A reversing timing is set by a stopper or the pressing numberof times of the switch 38.

FIG. 39 is a characteristic diagram of a direction change ofelectromagnetic waves 42 by the rotary waveguide 8 of FIG. 38. Thediagram is obtained by converting the direction change to a movement ofa point 81 of the emission port 17. The bottom face of the heatingchamber 4 is represented by xy coordinates. (0, 0) in the xy coordinatesis the center of the bottom face of the heating chamber 4. By way ofexample, supposing that a distance between the first and second rotaryshafts 69 and 72, i.e., a radius of the revolution of the rotarywaveguide 8 around the shaft 69 is 70 mm, a distance from the center ofthe second rotary shaft 72 to the point 81, that is, a radius of therotation of the motor around the shaft 72 is 60 mm, and a rotation cycleis 1/10 a revolution cycle, coordinates of the point 81 are expressed byexpressions (2) and (3), and the point 81 assumes a spiral movement(cycloid) as in FIG. 39:

    x=70 cos θ+60 cos (10θ)                        (2)

    y=70 sin θ+60 sin (10θ)                        (3)

wherein θ is an angle of the revolution. While the motor 18 isconstituted to reverse when it reaches either of the end faces 79 and 80as mentioned earlier, this is neglected in FIG. 39.

FIGS. 40-42 show a 10th embodiment of the present invention as animprovement of the 9th embodiment.

The rotary waveguide is constructed in two stages according to the 10thembodiment. A rotating ratio of the two stages of the rotary waveguideis set by a gear ratio of gears when the rotary waveguides rotate andrevolve.

The structure of the apparatus will be depicted with reference to FIG.40 and FIG. 41 which shows an essential part of FIG. 40.

A gear 82 is rotated interlockingly with the first rotary shaft by themotor 18, and a gear 83 is rotated (around its own axis) by the gear 82.A gear 84 is integral with the gear 83, and therefore operates the sameas the gear 83. When the gears 84 and 83 rotate together around thesecond rotary shaft 72, the gears 84, 83 and the second rotary shaft 72are revolved around the gear 82 by the gear 85.

A coupling part 87 of a first rotary waveguide 86 is provided in theperiphery of the first rotary shaft 69, with a coupling part 89 of asecond rotary waveguide 88 set inside the second rotary shaft 72.Therefore, the electromagnetic waves emitted from the magnetron 2 aretransmitted sequentially from the waveguide 3, coupling part 87, firstrotary waveguide 86, coupling part 89 to the second rotary waveguide 88.The embodiment has a merit that distances between the magnetron 2 andcoupling part 87 and between the coupling part 87 and coupling part 89are kept constant at all times, independently of the rotation of therotary waveguides.

As a result, the electromagnetic waves run a constant distance, whichfacilitates the matching and enhances the heating efficiency.

For positioning of the rotary waveguides in the embodiment, a stopper 90is employed. A reference position is determined by butting the gear 84to the stopper 90.

When a stepping motor is used, it is a simple way to drive the motor toa target position if the motor is started again after sent to thereference position.

In other words, a sufficiently larger number of pulses are input todrive the motor to the reference position, and thereafter a requirednumber of pulses should be input.

When the rotation cycle is set to be 1/6 the revolution cycle by thegear ratios, the rotary waveguides draw a locus as shown in FIG. 42.

FIGS. 43 and 44 are sectional views of an essential part of a highfrequency heating apparatus according to an 11th embodiment of thepresent invention. The apparatus includes, as a driving part, the motor18 with a rotary shaft 91 below the waveguide 3, a holding part 92, adriving shaft 93 and a fixing member 94. When the rotary shaft 91 of arectangular cross section rotates, the driving shaft 93 having arectangular opening fitted in a movable fashion in a vertical directioninto the rotary shaft 91 rotates. Since there is a male screw 95 outsidethe driving shaft 93 and a female screw 96 inside the holding part 92,the driving shaft 93 moves up or down depending on the rotatingdirection of the motor 18. Therefore, the direction of theelectromagnetic waves 42 from the emission port 17 of the rotarywaveguide 8 can be controlled not only in a circumferential direction ofthe motor 18 by the rotation of the motor, but in the vertical directionby the movement of the driving shaft 93. FIG. 43 shows a state in whichthe driving shaft 93 is raised and FIG. 44 shows a descended state.

A combination of the rotational and vertical movements of the rotarywaveguide 8 is utilized in the above 11th embodiment. The rotarywaveguide 8 can be naturally controlled in two-dimensions orthree-dimensions in other manners, e.g., by a combination of theoperation of the turntable 1 and the spiral movement of the rotarywaveguide discussed earlier.

A 12th embodiment of the present invention will now be described withreference to FIGS. 45 and 46. FIG. 45 is a sectional view indicating theconstitution of a high frequency heating apparatus of the embodiment andFIG. 46 is an enlarged view of an essential part of the apparatus.

According to the 12th embodiment, an opening position variation means isprovided as the local heating means, and a turntable is not used. InFIG. 45, the electromagnetic waves from the magnetron 2 heat via thewaveguide 3 the food 6 on the saucer 21 set inside the heating chamber4. A position of an opening part connecting the waveguide 3 with theheating chamber 4 to guide the electromagnetic waves is determined by afirst shielding plate 97 and a second shielding plate 98. That is, acombination of a notched part 99 in the first shielding plate 97 and anotched part 100 in the second shielding plate 98 determines theposition of the opening part.

The first shielding plate 97 is rotated around a shaft 102 by therotation of a first stepping motor 101 which is the opening positionvariation means. The first stepping motor 101 rotates a first rotaryshaft 103, whereby a first gear 104 of the first rotary shaft 103 isrotated. A gear formed in the periphery of the first shielding plate 97is rotated along with the rotation of the first gear 104. A secondstepping motor 105 rotates a second rotary shaft 106, and consequently asecond gear 107 of the second rotary shaft 106 is rotated. A gear in theperiphery of the second shielding plate 98 is also rotated in accordancewith the rotation of the second gear 107.

FIG. 46 is an enlarged view of the shielding plate, specifically, FIG.46(a) showing the first shielding plate 97 and FIG. 46(b) the secondshielding plate 98. Both of the shielding plates are circular as isclear from FIG. 46. The notched part 99 is formed in a radial directionof the first shielding plate 97, and the notched part 100 is spiralrunning from the center to the periphery of the second shielding plate98. The two shielding plates are arranged up and down, so that theopening part can be formed at an optional position within the circle ofthe shielding plates. In other words, an optional position in the wholearea within the heating chamber 4 can be utilized as the opening partthrough which the electromagnetic waves are emitted for local heating.Moreover, if the shielding plates 97 and 98 are rotated with differentcycles, the opening part is sequentially changed in position in theheating chamber 4, so that the whole area can be heated uniformly.

The control means 19 drives the shielding plates 97, 98 with differentcycles at the initial stage when the heating is started, i.e., uniformheating is carried out. The control means 19 extracts thelow-temperature portion of the food 6 based on the temperaturedistribution detected by the temperature sensor 26, thereby controllingangles of the two shielding plates 97, 98 to position the opening partbelow the low-temperature portion. The uniform heating for the wholefood 6 without the low-temperature portion is realized by repeating theabove control.

Although two motors are employed to drive the two shielding plates inthe above embodiment, it is possible to change gear ratios by one motor,which is effective to improve the reliability with the driving partsreduced. Besides, the shielding plates may be driven linearly, notrotated, or many opening parts may be formed and equipped with shieldingplates respectively.

In the foregoing first through 12th embodiments, the emission port oropening which is the position through which the electromagnetic wavesare emitted by the local heating means is set at the bottom face of theheating chamber 4. This is because it is effective to emit andconcentrate the electromagnetic waves as closely as possible to aportion of the food in order to locally heat the portion. However, theposition of the emission port or opening is not limited to the bottomface according to the present invention and, the emission port oropening may be formed at a top face or side face. In the case where theopening is formed at the top face, either the food or the top face ismoved in a vertical direction, so that the food and top face are closeto each other to exert more effective control of heating. Moreconcentrated local heating is accomplished in this way because of theabsence of a saucer or stage between the opening and the food. If theopening is formed at the side face, the food is moved toward a side faceat the side of the rotary waveguide or the side face is moved towardsthe food, so that the food and the side face at the side of the rotarywaveguide are close to each other, making it possible to control in avertical direction and locally heat the high food. Alternatively,emission ports or openings may be provided at two or more of the bottomand side faces of the heating chamber to variably control the heatingdistribution. This control is useful for large-size food.

Eventually, for local heating, the emission port or opening should bedriven while in a state close to the food.

In the first through 12th embodiments, if the temperature distributiondetection means is constituted of one infrared detection element therebyto detect the two-dimensional temperature distribution, the detectionmeans is inexpensive and the output of the infrared detection elementcan be simply adjusted. However, driving the one infrared detectionelement does not limit the present invention. For example, a pluralityof infrared detection elements may be arranged in two dimensions todetect the temperature distribution, which effectively improves thereliability because of the elimination of driving parts and realizesinstantaneous detection of the temperature distribution. Moreover, aplurality of infrared detection elements may be linearly arrangedthereby to detect a linear temperature distribution which is in turncombined with the rotation of the turntable thereby to detect atwo-dimensional temperature distribution. In a different way, aplurality of the infrared detection elements disposed linearly may beshaken to detect the two-dimensional temperature distribution. The sameeffect is obtained in any method.

Although one waveguide runs from the magnetron to the emission part, thewaveguide may be diverged in many directions and each is provided withthe emission part. More delicately controlled local heating is realizedby switching the emission parts.

A coaxial line may be employed instead of the waveguide.

Further, a semiconductor oscillation device may be used instead of themagnetron.

A 13th embodiment of the present invention will be discussed withreference to FIGS. 47-51. FIG. 47 is a sectional view showing theconstitution of a high frequency heating apparatus in the 13thembodiment. FIG. 48 is a view particularly showing a detectioncharacteristic of a physical amount detection means in the embodiment,and FIG. 49 is a sectional view of an essential part of the physicalamount detection means. FIG. 50 is a block diagram explanatory of acontrolling operation in the embodiment. FIG. 51 is a diagram of atemperature change characteristic in the embodiment.

The turntable 1 is rotated with a constant cycle by the motor 22 as arotating means. A rotational center of the motor 22 is approximately atthe center of the bottom face of the heating chamber 4, while arotational center of the motor 18 is shifted from the center of thebottom face of the heating chamber 4, i.e., approximately in the middleof the center and a peripheral edge of the bottom face of the heatingchamber. Because of this positional relationship, the heated portion ofthe food in the radial direction of the turntable 1 can be changed bythe rotary waveguide 8. That is, an optional position on the saucer 21can be heated in association with the rotation of the turntable 1.

The temperature sensor 26 is provided with the opening 29 for securingan optical path at the top face of the heating chamber 4. In thevicinity of the opening 29 is disposed a choke structure 108 not to leakthe electromagnetic waves outside the heating chamber 4.

The temperature sensor 26 will be described more in detail. FIG. 48 is asectional view taken along the line B-B' of FIG. 47. The opening 29 isformed at a ceiling face or top face 109 of the heating chamber 4. Thechoke structure is constituted of two sheet metals 110a and 110b. Thesheet metal 110a constituting the optical path is a cylindrical metallicpart spreading at the top face 109 and in tight contact with the topface 109. The sheet metal 110b is a box-like part with a small hole 111and in tight contact with the top face 109. The infrared rays from theheating chamber 4 are let outside through the small hole 111 due to thechoke structure, but the electromagnetic waves in the heating chamber 4are shielded and hardly leak outside. If a height L of the chokestructure is set to be λ/4 in FIG. 48, specifically, about 30 mm whenthe frequency is 2.45 GHz, the impedance at the small hole 111 becomesindefinite, thus exerting the maximum effect to shut the electromagneticwaves.

In FIG. 48, a pyroelectric infrared detection element 112 detects theentering amount of infrared rays, that is, generates an outputcorrelative to a temperature at a position in the heating chamber 4 thatis a view field. The infrared detection element 112 is fixed to theinterior of a fixed member 113 and detects the temperature in a narrowrange through the reduced view field of a lens 114 fitted to the fixedmember 113. The lens 114 is a Fresnel lens 114 formed of a materialpassing infrared rays. A stepping motor 115 rotates a small gear 117 anda chopper 118 about a first rotary shaft 116.

The chopper 118 constitutes a slit, rotating while opening and closingthe optical path to the infrared detection element 112. The small gear117 is kept in touch with a large gear 119 which has a second rotaryshaft 120 fitted thereto. The second rotary shaft 120 is renderedrotatable via a receptacle 121. Electronic circuits (not shown) such asan amplifier circuit and the like in addition to the infrared detectionelement 122 are mounted to a printed circuit board 122 set to the secondrotary shaft 120. These parts are accommodated in a metallic case 124having a small hole 123 at a position of the optical path for theinfrared rays, covered with a metallic lid 125 and fixed to the chokestructure 110 by the metallic lid 125.

In the constitution as above, the stepping motor 115 oscillates theinfrared detection element 112 from front to back in FIG. 48, andsimultaneously with this the optical path is opened and closed by thechopper 118. An oscillation cycle of the infrared detection element 112is set to be an integral fraction of a rotating cycle of the motor 22,in other words, the rotating cycle of the motor 22 is set to be anintegral multiple of the rotating cycle of the infrared detectionelement 112. Accordingly, the temperature of the same position can bedetected every rotation of the motor 22.

A detection position by the infrared detection element 112 is indicatedin FIG. 49. A detection field by the infrared detection element 112 isindicated by a small circle and a locus of the center of the detectionfield is indicated by a broken line. In the example of FIG. 49, atemperature detection point is changed five times in one way of thereciprocative oscillation of the infrared detection element 112. Thedetection position covers all over the whole saucer 21 because of thecombination of the oscillation of the infrared detection element 112 andthe rotation of the motor 22, and accordingly the temperaturedistribution is detected in two dimensions. Since the motor 22 isrotated with the cycle of an integral multiple of the oscillation cycleof the infrared detection element 112, a temperature difference from thetemperature one cycle earlier during the rotation of the turntable or atemperature change from the initial temperature can be detected at everydetection position.

The control operation by the control means 19 will be depicted withreference to FIG. 50. The control means 19 controls the motor 18 basedon the temperature distribution detected by the temperature distributiondetection means 26. An extraction means 126 distinguishes for everydetection position whether the detected temperature shows thetemperature of the food 6 or the saucer 21 or a wall face of the heatingchamber 4. Since it is not known how large the food 6 is or where thefood 6 is located, etc. at the initial stage of heating, a uniformheating control means 127 controls the motor 18 in the first place. Theuniform heating control means 127 rotates the motor 18 with a cycleshorter than the rotating cycle of the motor 22, reverses or,reciprocates the motor 18 after rotating half, drives at random, etc.,so that the electromagnetic waves are stirred and uniformly distributedin the heating chamber 4. Whether or not the detected temperature showsthe temperature of the food 6 is distinguished from the temperature riseat every detection position while the motor 18 is controlled by theuniform heating control means 127.

FIG. 51 is a graph of a surface temperature change of the food 6 and atemperature change of other parts than the food 6, e.g., saucer 21 orthe like when the uniform heating control means 127 controls the motor18. An axis of abscissa shows the time t passing after the start ofheating and an axis of ordinate indicates a temperature change ΔT fromthe start of heating. More specifically, an area C indicated byslantwise lines shows the temperature change of other parts than thefood 6, and an area D shows the temperature change of the food 6. Sincethe saucer 21 has a smaller dielectric loss than the food 6 and is hardto absorb the electromagnetic waves, the temperature of the saucer 21hardly increases as is shown in FIG. 51. Accordingly, the food 6 and theother parts than the food 6 can be clearly distinguished from eachother. A temperature change operation means 128 stores, for instance,temperatures corresponding to detection positions in the first cycle ofthe rotation of the motor 22 from the start of heating, and operates thetemperature difference ΔT between a temperature at the detectionposition t13 later and the temperature at the same position in the firstcycle. A temperature change comparison means 129 judges that it is thetemperature of the food 6, when the temperature difference ΔT operatedby the operation means 128 is larger than a preset predetermined valueΔT1, or it is the saucer 21 if the temperature difference ΔT is smallerthan the predetermined value ΔT1.

Once the extraction means 126 distinguishes whether it is the food 6 orthe saucer 21 at each detection position, a heating mode switch means130 switches from the uniform heating control means 127 to a localheating control means 131 to control the motor 18. The local heatingcontrol means 131 stops the motor 18 at a suitable position thereby tocontrol a point where to concentrate the electromagnetic waves. Alow-temperature portion extraction means 132 extracts a low-temperatureportion among the detection positions judged to be the food 6 by theextraction means 126. The local heating control means 131 controls todrive the motor 18 so that the electromagnetic waves are emitted to thelow-portion extracted by the extraction means 132. When theelectromagnetic waves are emitted to the low-temperature portion of thefood 6 by the local heating control means 131 to remove thelow-temperature portion and if the whole of the food 6 becomes a uniformtemperature, the motor 18 is controlled again by the uniform heatingcontrol means 127.

The low-temperature portion extraction means 132 stores as a heatingposition a position of the lowest detected temperature among thedetection positions judged to be the food 6 by the extraction means 126in one reciprocation of the infrared detection element 112. While thereciprocative oscillation of the infrared detection element 112 isrepeated in one rotation of the motor 22, the detected heating positionsduring the oscillation are all stored. When the motor 22 is rotated, anangle of the motor 18 is adjusted by the local heating control means 131toward the stored heating position in the radial direction above therotary waveguide (emission part) 8, so that the heating position,namely, the low-temperature portion of the food 6 is heated. Byrepeating this control, the low-temperature portion is eliminated fromthe food 6 and the food 6 is heated uniformly.

As a simple way to reduce the driving number of times of the motor 18,the detection positions by the infrared detection element 112 arearranged on concentric circles. Whether it is the food 6 or the saucer21 is distinguished for every circumference of the concentric circles,the maximum temperature is extracted for each circumference judged to bethe food 6, the circumference of the lowest maximum temperature isextracted by the low-temperature portion extraction means 132, and theangle of the motor 18 is adjusted to concentrate the electromagneticwaves onto the extracted circumference. The durability of the motor 18is improved in this method.

Meanwhile, the "uniform" in the uniform heating control means 127represents heating of a wide area in contrast to the local heating, notimplying heating in a perfectly uniform manner not generatingirregularities.

The physical amount detection means is the temperature distributiondetection means in the 13th embodiment, but is not limited to the meansin the present invention. For example, a solid image pick-up devicecalled as a CCD image sensor capable of recognizing the shape or colorof the food 6 may be used and, in this case, the control means controlsthe local heating means based on the color changing in accordance withthe progress of heating and a color distribution. Concretely, in thecase of meat, the local heating means is controlled so as to finish thewhole meat light brown while monitoring the color changing from red,light brown finally to white. Alternatively, the local heating means maybe controlled by the control means based on a change of the shape. Forexample, since a rice cake becomes soft and swells, the local heatingmeans is controlled to let the whole rice cake swell equally. The sameeffect is obtained even when a plurality of light emitting elements andphotodetecting elements are used thereby to recognize the shape of thefood from a shut pattern of the optical path. If an optimum controlpattern for the local heating means is preliminarily storedcorrespondingly to the shape of the food, the control means can controlthe local heating means simply by the initial recognition of the shapeby the solid image pick-up device or a plurality of light emittingelements and photodetecting elements. Furthermore, if the optimumcontrol pattern for the local heating means is stored beforehand inconformity with the menu and weight, the weight sensor can be thephysical amount detection means.

The control means in the 13th embodiment is composed of the uniformheating control means, the local heating control means and the heatingmode switch means. The present invention is not restricted to this. Anexample wherein the uniform heating control means and the heating modeswitch means are eliminated will be described with reference to FIG. 52.FIG. 52 is a block diagram explaining the control operation in the highfrequency heating apparatus. The extraction means 126 distinguisheswhether it is the food 6 or the saucer 21 at the start of heating. Thetemperature change comparison means 129 carries out comparisons everymoment with a predetermined temperature change determined by the passingtime. When the temperature change is larger than the predeterminedtemperature change, it is judged to be the food 6. If the temperaturechange is smaller than the predetermined temperature change, it isjudged as the saucer 21. The predetermined temperature change isindicated by a line E in FIG. 51 as a function determined by the passingtime. The temperature change of the food 6 is small at the early stageof heating, and therefore the food 6 and the saucer 21 may be possiblyincorrectly distinguished. However, the error is corrected in accordancewith the progress of the heating, therefore not influencing large to thetotal heating distribution.

According to a different method, the motor 18 is fixed at apredetermined position at the initial stage of heating. Generally, sincethe food 6 is placed at the center of the heating chamber 4 in manycases and the food is often in such a shape that the periphery is easyto heat whereas the center is hard to heat, the rotary waveguide(emission part) 8 is first fixed in direction as shown in FIGS. 12 and25. Although the initial optimum heating position may not be possiblycorrect even in this method, the error is corrected as the heatingproceeds, without adversely influencing the total heating distributiongreatly. Even if the motor 18 is initially fixed not at the center, butin the periphery as shown in FIGS. 13 and 26 or at other positions thanthe center, the heating position is properly controlled in accordancewith the progress of heating, resulting in the same effect.

A 14th embodiment will be described with reference to FIG. 53. FIG. 53is a block diagram explanatory of the control operation of a highfrequency heating apparatus according to the 14th embodiment, in whichthe parts in the same constitution as in the 13th embodiment are denotedby the same reference numerals. A menu setting means 133 has keyscorresponding to cooking menus, e.g., a "warming" key 133a, a"defrosting" key 133b, a "milk" key 133c, etc. A cooking menu is setwhen the user depresses any of the keys. A control mode selection means134 is to select either of a heating mode switch means 135 and a heatingmode non-switch means 136 to control the motor 18 in conformity with thecooking menu set by the setting means 133. The heating mode switchcontrol means 135 operates to control the motor 18 in the manner asdescribed in the foregoing 13th embodiment. That is, the motor 18 isfirst controlled by the uniform heating control means 127 at the heatingstart and, after the extraction means 126 distinguishes the food 6 fromthe saucer 21, the motor 18 is controlled by the local heating controlmeans 131 for the low-temperature portion detected by thelow-temperature portion extraction means 132. On the other hand, theheating mode non-switch control means 136 controls the motor 18 with theuse of only the local heating control means 131 from the start ofheating.

In order to reheat cold rice, boiled and seasoned substance or grilledsubstance, the food should be locally concentratedly heated and theheated portion should be controlled and changed to obtain the uniformtemperature distribution as a whole. The same applies to defrosting ofmeat and fish. In contrast, when a liquid substance such as milk or thelike is intensively heated from below a container containing thesubstance, the substance is uniformly heated in a vertical directionbecause of the convection. Therefore, supposing that the substance orfood is usually placed at the center of the heating chamber 4, the motor18 should be controlled to fixedly position the emission part 8 tolocally heat the central portion of the food in the case of liquidsubstance, as shown in FIGS. 12 and 25. If the food is not set at thecenter of the heating chamber, the extraction means 126 detects theposition of the container and the motor 18 is controlled to fix theposition of the emission part 8 to agree with the container. If aplurality of containers are placed on concentric circles, the motor 18is controlled to fix the emission part 8 so as to locally heat theconcentric circles. If the plurality of containers are not arranged onconcentric circles, the motor 18 is controlled to change the directionof the emission part 8 each time to match with the position of thecontainer passing in the vicinity of the emission part 8.

When the user presses the key to set a cooking menu, the control modeselection means 134 selects the heating mode switch means 135 if thepressed key is the "warming" key 133a or "defrosting" key 133b, wherebythe uniform heating control means 127 controls the motor 18 at theinitial stage of the heating, and afterwards the local heating controlmeans 131 controls the motor 18. If the key manipulated by the user isthe "milk" key, the control mode selection means 134 selects the heatingmode non-switch means 136. In this case, the local heating control means131 first controls the motor 18 thereby to fix the emission part 8 tolocally heat the center of the heating chamber 4. If the extractionmeans 126 recognizes that the container of the milk is located at thecenter of the heating chamber, the local heating to the center of theheating chamber is continued as it is. If it is recognized that the milkcontainer is not at the center of the heating chamber or a plurality ofcontainers are present, the motor 18 is controlled to set the positionof the emission part 8 so that the center of the detected position ofthe milk container is locally heated.

In the case where the milk container is not at the center of the heatingchamber, the magnetron may be stopped in a time interval while thecontainer is separated away from the emission part 8 by the rotation ofthe turntable, thus refraining the electromagnetic waves from enteringthe heating chamber 4. Although this consumes time for heating, thetemperature distribution is improved further and the energy is notwasted. Sake, miso soup, coffee and the like can be handled in the samemanner as milk by adding these as menus to be set by the menu settingmeans 133.

A 15th embodiment will be described with reference to FIGS. 54 and 55.FIG. 54 is a sectional view indicating the constitution of a highfrequency heating apparatus of the 15th embodiment and FIG. 55 is asectional view of an essential part of a temperature distributiondetection means of the embodiment, in which parts in the sameconstitution as in the foregoing embodiments are designated by likereference numerals and the description thereof is omitted.

In the 15th embodiment, the turntable motor as a rotating means is notemployed. The electromagnetic waves from the magnetron 2 are, via thewaveguide 3 and power feed chamber 15, sent into the heating chamber 4to heat the food 6 in the heating chamber 4. The emission part 8 isprovided in the power feed chamber 15, and rotated by the motor 18 whichis the moving means for the waveguide. The power feed chamber 15 iscovered with the cover 25. The stepping motor 18 rotates a first rotaryshaft 137 having a large gear 138. A peripheral gear 139 fixedly mountedto the waveguide 3 has a gear formed therein and a groove as a bearingfor a small gear 140. The small gear 140 is held in touch with the largegear 138 and peripheral gear 139. A second rotary shaft 141 fitted tothe small gear 140 is rotatably held by the groove formed in theperipheral gear 139 as the bearing. The emission part 8 is mounted tothe second rotary shaft 141. When the motor 18 is rotated in the aboveconstitution, the second rotary shaft 141, while repeatedly rotating,moves in the periphery of the large gear 138 along the peripheral gear139. The motor 18 is initially registered by an origin detection switchor a stopper, etc. A moving angle of the motor 18 from the initialposition is sequentially accumulated, so that the rotating angle of themotor 18 is always detected, from which the position and direction ofthe emission part 8 are detected.

FIG. 55 is the sectional view taken along the line F-F' of FIG. 54, inwhich parts of the same constitution as in the 13th embodiment in FIG.48 are denoted by the same reference numerals and the description of theparts is omitted. The stepping motor 115 oscillates the infrareddetection element 112 from front to back of FIG. 55 and at the sametime, opens and closes the optical path by means of the chopper 118. Adriving means 142 is constituted of a stepping motor for driving thewhole metallic case 124 including the infrared detection element 112.The stepping motor 142 rotates a rotary shaft 143, thereby driving acoupling part 144 fitted to the rotary shaft 143 to oscillate theinfrared detection element 112 right and left in FIG. 55. An oscillationcycle of the stepping motor 142 is a sufficiently small integralmultiple of the oscillation cycle of the stepping motor 115. Thetemperature of the same position can hence be detected every onereciprocation of the stepping motor 142. In the thus-constitutedapparatus, the temperature of the whole area in the heating chamber 4 isdetected and the two-dimensional temperature distribution is obtained.Since the temperature of the same position can be detected everyreciprocation of the stepping motor 142, the temperature difference fromthe previous temperature or the temperature change from the initialtemperature can be calculated for each detection position.

The control means 19 initially rotates the motor 18 with a constantcycle to uniformly heat the food. After the food is extracted, thecontrol means 19 extracts the low-temperature portion in the extractedfood and controls the angle of the motor 18 to direct the emission part8 to the low-temperature portion. The low-temperature portion is thuseliminated from the food 6 by repeating the above operation, so that thefood can be totally heated to a uniform temperature. In the embodiment,since the food 6 is not rotated, the food is allowed to be heavy inweight and the space in the heating chamber 4 can be efficientlyutilized. While both the position and the direction of the emission part8 are controlled by one motor in the description of the 15th embodiment,this arrangement does not limit the present invention. The direction andthe position of the emission part 8 may be controlled separately bydifferent motors, or controlled linearly by a biaxial movement, whicheffects more carefully controlled local heating.

A 16th embodiment of the present invention will be discussed withreference to FIGS. 56 and 57 respectively showing a sectional view of ahigh frequency heating apparatus and a sectional view of an essentialpart of an electromagnetic wave emission part of the apparatus. Thoseparts in the same constitution as in the 13th-15th embodiments aredesignated by the same reference numerals, the description of which isomitted here.

The opening position variation means is provided as a distributionvariation means according to the 16th embodiment. In FIG. 56, theelectromagnetic waves emitted from the magnetron 2 heat the food 6 onthe saucer 21 in the heating chamber 4 via the waveguide 3. The openingpart connecting the waveguide 3 with the heating chamber 4 and guidingthe electromagnetic waves to the heating chamber has a first opening 145and a second opening 146 respectively arranged closer to the center ofthe heating chamber 4 and closer to the periphery of the heating chamber4. The first and second openings 145 and 146 are aligned in the radialdirection of the rotary turntable 1. Either of the openings 145 and 146is shut by a shielding plate 147. The shielding plate 147 is asemi-circular metallic plate and rotated by a rotary shaft 148 of amaterial of a low dielectric loss hard to absorb electromagnetic waves.The opening position variation means 18 consisting of a stepping motorshuts either one of the openings 145 and 146 by rotating the rotaryshaft 148. A position through which the electromagnetic waves areradiated into the heating chamber 4 is changed in the aboveconstitution. A portion of the food 6 immediately above the opening notshut by the shielding plate is intensively heated. The food 6 can beuniformly heated if the shielding plate 147 is rotated with a constantcycle.

FIG. 57 is a sectional view taken along the line G-G' of FIG. 56. Theopenings 145 and 146 are rectangular and, the bottom face of the samerectangular heating chamber 4 is parallel to four sides of each opening.In FIG. 57(a), the electromagnetic waves are emitted from the secondopening 146 into the heating chamber 4, with the first opening 145 beingshut by the shielding plate 147 in the same manner as in FIG. 56, andconsequently a portion of the food in the periphery of the heatingchamber 4 is locally heated. On the contrary, in FIG. 57(b), the secondopening 146 is shut by the shielding plate 147 and the electromagneticwaves are emitted through the first opening 145 to the heating chamber4, whereby a portion of the food 6 in the vicinity of the center of theheating chamber 4 is locally heated.

The control means 19 initially rotates the shielding plate 147 with aconstant cycle to achieve uniform heating. Once the food 6 is extractedbased on the temperature distribution detected by the temperature sensor26, the low-temperature portion of the food 6 is extracted and stored asa position to be heated. The position of the shielding plate 147, i.e.,openings 145, 146 is changed every moment by rotating the turntable 1 toagree with the to-be-heated portion of the food in the radial direction.The control of optimum local heating is carried out in this manner.Since the low-temperature portion is removed by repeating the aboveprocess, the food 6 is uniformly heated as a whole.

In this embodiment, two openings are provided and opened and closed bythe rotation of the semi-circular metallic plate. By so doing, thestructure becomes simple and compact. However, the present invention isnot limited to this structure. The number of the openings may beincreased to more delicately control the uniform heating. The shieldingplate may not be rotated, but may be moved linearly. Or a plurality ofopenings may be formed and each opening is equipped with the shieldingplate.

A 17th embodiment of the present invention will be described withreference to FIGS. 58 and 59. FIG. 58 is a block diagram explanatory ofthe control operation of a high frequency heating apparatus according tothe 17th embodiment and FIG. 59 specifically shows a temperaturecharacteristic diagram of an outline extraction means. Parts of the sameconstitution as in the 13th-16th embodiments are denoted by the samereference numerals in the drawings and the description thereof isomitted here.

Referring to FIG. 58, in the initial state of heating, the local heatingmeans 16 is controlled by the uniform heating control means 127. When itis distinguished whether or not the food is present at each detectionposition by the temperature distribution detection means 26, theextraction means 126 switches the uniform heating control means 127 tothe local heating control means 131 by the heating mode switch means 130to control the local heating means 16.

The extraction means 126 is constituted of a temperature changeoperation means 128 and an outline extraction means 149. The temperaturechange operation means 128 storing temperatures corresponding todetection positions obtained by the temperature distribution detectionmeans 26 at the start of the heating operates the temperature differenceΔT between the temperature at the detection position a predeterminedtime later and the initial temperature at the same detection position.The outline extraction means 149 extracts an outline of the food basedon the temperature change ΔT at each detection position.

In FIG. 59(a), each square represents a detection position by thetemperature distribution detection means 26 and a hatched part is thefood 6. The temperature distribution detection means 26 consists of aplurality of infrared detection elements arranged in two dimensions orlinearly. The temperature distribution is detected at detectionpositions in a matrix by oscillating the infrared detection elements.The temperature change of the food 6 from the start of the heating isnormally larger than that at positions where the food is not present. AnX direction differentiation means 150 operates a difference oftemperature changes in the X direction of detection positions arrangedin a matrix, namely, detection positions adjacent to each other in alateral direction in FIG. 59, and stores detection positions larger thana predetermined value of the difference. Detection positions marked byslantwise lines in FIG. 59(b) are those larger than the predeterminedvalue and stored in the differentiation means 150. Similarly, a Ydirection differentiation means 151 operates a difference of temperaturechanges in the Y direction of detection positions arranged in a matrix,i.e., detection positions adjacent to each other in a longitudinaldirection in FIG. 59 and stores the detection positions larger than apredetermined value of the difference. Detection positions marked byslantwise lines in FIG. 59(c) are larger than the predetermined valueand stored in the differentiation means 151.

A shaping means 152 operates a logical OR of the detection positionsstored in the X direction differentiation means 150 and the detectionpositions stored in the Y direction differentiation means 151. That is,the detection positions stored in either of the differentiation means150 and 151 are judged to be the outline of the food. Although the fooditself shows a distribution in temperature rise and therefore a largetemperature difference exists between adjacent portions inside the food,the shaping means 152 judges the largest periphery as the outline of thefood. If the periphery is partly broken, the shaping means 152 connectsthe broken parts and forms the outline. The extraction means 126extracts the outline of the food as above. The inside of the outline isset as the food.

The low-temperature portion extraction means 132 extracts thelow-temperature portion from the food extracted by the extraction means126, and the local heating control means 131 controls the local heatingmeans 16 to radiate the electromagnetic waves to the low-temperatureportion extracted by the extraction means 132. Because of thisarrangement that the food to be heated is extracted and theelectromagnetic waves are emitted to the extracted food, the wastefulconsumption of energy is eliminated and the food is heated efficiently.

An 18th embodiment of the present invention will be described withreference to FIG. 60. FIG. 60 is a block diagram explanatory of thecontrol operation of a high frequency heating apparatus according to the18th embodiment, wherein parts in the same constitution as in the13-17th embodiments are designated by the same reference numerals, withthe description thereof being omitted.

The 18th embodiment is related to partial heating of food, for example,when a variety box lunch containing, in a box, a substance to be heatedsuch as rice or the like and a substance not to be heated such as rawfish called sashimi, pickles or the like is to be heated. According tothe 18th embodiment, only the rice is heated even if the whole lunch boxis put in the heating chamber.

In FIG. 60, the user manipulates a heating range setting means 153 toset a heating range. The heating range setting means 153 consists of asetting screen 154 of a liquid crystal, a cross-shaped cursor key 155, asetting key 156 and a cancel key 157.

The user sets an area or range to be heated among the bottom face of theheating chamber with regarding the bottom face as the setting screen154. The user first presses the setting key 156 to start setting. Afirst point 158 is displayed at an upper left comer of the settingscreen 154. Then, the user manipulates the cursor key 155 thereby tomove the first point 158 in the setting screen 154. The cursor key 155comprises an up key 155a, a down key 155b, a left key 155c and a rightkey 155d. The first point 158 can be moved vertically and horizontallyto an optional position by these keys. When the first point 158 is movedto an end of the heating range, the user presses the setting key 156.The first point 158 is accordingly fixed at the position, and a secondpoint 159 is displayed at the same position. The user manipulates thecursor key 155 in the same manner as above to move the second point 159.At this time, a rectangle 160 having the first point 158 and the secondpoint 159 on a diagonal line is displayed on the setting screen 154. Theuser moves the second point 159 to an optional position on the settingscreen 154, thereby setting the heating range by the rectangle 160. Whenthe setting key 156 is depressed again, the second point 159 and therectangle 160 are certainly set. In the case where there are a pluralityof ranges to be set, the user should press the setting key 156 again,when the first point 158 is displayed again on the setting screen 154,allowing the user to repeat the above procedures. If the usermanipulates erroneously, the cancel key 157 should be used, whereby thecontent set by the setting key 156 immediately before the error iscanceled.

In the manner as above, once the heating range is set by the user, thecontrol means 19 controls to heat the heating range uniformly. Thelow-temperature portion extraction means 132 extracts thelow-temperature portion from the heating range set by the setting means153 in accordance with a signal from the temperature distributiondetection means 26. The local heating control means 131 controls thelocal heating means 16 so as to radiate the electromagnetic waves to thelow-temperature portion extracted by the extraction means 132.Accordingly, the low-temperature portion is eliminated from the heatingrange and the whole of the heating range is heated uniformly. Since thefood outside the heating range is not heated, the food to be tasted atlow temperatures is left at low temperatures.

Although the above embodiment is directed to simultaneous heating of thevariety box lunch containing different kinds of stuff in one box, it isalso unnecessary to extract the to-be-heated stuff at the start ofheating once the heating range is set even if a single kind of stuff isto be heated. The control means is accordingly simplified inconstitution. While the heating range setting means 153 is constitutedof the setting screen 154, cursor key 155, setting key 156 and cancelkey 157 in the embodiment, the present invention is not restricted tothis constitution. For example, a touch panel or a mouse is utilizable,with the same effect achieved. Moreover, while the manipulation issimplified by setting the heating range by the rectangle, the sameeffect is obtained even when the setting range is set by a free curve.If the heating range is coded and printed by bar codes or the like on apackage of the variety box lunch, the heating range can be set simply byreading of the codes optically. In this case, even a complicated heatingrange can be set through a remarkably simple manipulation.

A 19th embodiment of a high frequency heating apparatus will be depictedwith reference to a block diagram of FIG. 61 explanatory of the controloperation of the apparatus. In the drawing, parts of the sameconstitution as in the 13th-18th embodiments are designated by the samereference numerals, the description of which is omitted.

The 19th embodiment is focused to a partial heating of food, similar tothe above 18th embodiment, for instance, when a packed lunch is heatedfor a customer over the shop counter. In general, kinds of productsserved in this fashion are limited, e.g., variety box lunch, grilledmeat box lunch, salmon box lunch, etc. and every stuff of the same kindis arranged at the same position in boxes. For example, the rice andgrilled meat of a grilled meat box lunch are filled at respective fixedpositions in the box. Since the apparatus is supposed to repeat heatingof products of the same kind many times although there is only a limitednumber of kinds, if the heating range for each kind of the products isregistered with a corresponding code, for example, "1" for the varietybox lunch, "2" for the grilled meat box lunch, "3" for the salmon boxlunch and the like, the heating range for the product selected by thecustomer can be set simply by the registered code.

The heating range setting means 153 in FIG. 61 consists of a group ofnumeral keys 161 from "1" to "10", a registration key 162 as aregistering means and a call key 163 as a registration calling means. Inregistering the heating range, first, the cursor key 155 and the settingkey 156 are manipulated to set the heating range in the manner asdescribed in the 18th embodiment. Thereafter, the registration key 162is depressed and any numerical key in the group 161 is pushed. Upondepression of the setting key 156, the heating range is stored alongwith the code set by the numerical key in a registration memory means164. In order to read out the heating range, the call key 163 isdepressed and the numerical key in the group 161 corresponding to theproduct is depressed. The heating range stored in the memory means 164correspondingly to the code of the pressed numeral key is displayed atthe setting screen 154. The setting key 156 should be depressed forconfirmation. Once the heating range is registered, the heating rangecan be set afterwards by the calling operation alone.

When the heating is started, the control means 19 controls the localheating means 16 and heats the heating range at a uniform temperature,similar to the 18th embodiment. More specifically, the low-temperatureportion extraction means 132 extracts the low-temperature portion fromthe heating range set by the setting means 153 based on the signal fromthe temperature distribution detection means 26, and the local heatingcontrol means 131 controls the local heating means 16 so as to emit theelectromagnetic waves to the low-temperature portion extracted by theextraction means 132.

The registering means and the calling means consist of the numerical keygroup 161, registration key 162 and call key 163 in the 19th embodiment.The present invention is not restricted to the above. For instance,codes of manipulation procedures, numeric codes or alphabetical codesmay be indicated on the setting screen 154 to be selected by the cursorkey 155 or setting key 156. In this case, the number of keys is reducedand the structure is simplified. Alternatively, codes may be printed onthe packages of products to be read optically, with the above numericalkey group eliminated, whereby the user can readily manipulate.

FIG. 62 is a sectional view of the constitution of a high frequencyheating apparatus according to a 20th embodiment of the presentinvention. The 20th embodiment is an applied example of the 9thembodiment shown in FIG. 37. The electromagnetic waves from themagnetron 2 are emitted to the heating chamber 4 via an opening 165through the waveguide 3. The turntable 1 on which the food 6 is loadedis spirally driven. Accordingly, the food 6 itself is positioned in theembodiment, and the direction of electromagnetic waves entering the food6 is changed by the position of the food 6. The embodiment is arepresentative example of switching the heated position, e.g., to heatthe center of the food 6 or the periphery of the food. The cam 37 andswitch 38 are the position detection part for detecting the position ofthe food.

FIGS. 63 and 64 are sectional views of an essential part of a highfrequency heating apparatus in a 21st embodiment of the presentinvention. The embodiment is different from FIGS. 43 and 44 in that thefood 6 is positioned, and also different from FIG. 62 in that thedirection of electromagnetic waves is controlled not only in twodimensions by the rotation of the turntable 1, but by the verticalmovement of the turntable, that is, the direction of the electromagneticwaves is controlled in three dimensions. FIG. 63 indicates a state wherethe turntable is raised and FIG. 64 is a state where the turntable isdescended.

A combination of the rotation and vertical movements of the turntable isdescribed here as a representative example of the three-dimensionalcontrol, for the sake of brevity. Needless to say, a spiral movement orthe like other arrangement may be adopted or combined with the above.

Further, although it is not necessary to limit the switching number oftimes of the heating distribution, heating irregularities are lessgenerated if the heating distribution is switched as many times aspossible.

FIG. 65 shows the constitution of an essential part, namely, turntable 1of a high frequency heating apparatus in a 22nd embodiment of thepresent invention, seen from below. The turntable in FIG. 65 which isdifferent from FIG. 17 is made of a permeable material which is hard toabsorb electromagnetic waves, e.g., ceramic or the like. The turntable 1consists of a disk 166 and the rotary bearing 48 in such constitution asto easily pass the electromagnetic waves even without an opening.

When the electromagnetic waves are sent from below, the turntable 1serves as a path for the electromagnetic waves. In the case where themicrowave oven is provided with the heater 28, the devised turntable ofFIGS. 17, 65 allows the electromagnetic waves to pass therethrough whilekeeping the heat-proof properties to the heater.

FIG. 66 is a sectional view of an essential part of a high frequencyheating apparatus according to a 23rd embodiment of the invention,specifically showing a dimensional relationship of the turntable 1 and acentral part 167 at the bottom face of the heating chamber 4. Theturntable 1 has a radius of r (a diameter of 2r in FIG. 66) and theupwardly projecting central part 167 at the bottom face of the heatingchamber 4 has a radius of R (a diameter of 2R in FIG. 66). Since 2R>2r,that is, R>r is held, even if the water is spilt on the turntable 1, itis prevented that the water runs down along the shaft of the turntable 1to leak out of the heating chamber 4. Moreover, the water is gatheredoutside the projecting central part 167, making it possible to wipe thewater without detaching the turntable. Particularly when the turntable 1is formed of ceramic as in FIG. 65, although some sort of improvementshould be devised to secure the durability of the turntable to preventthe turntable from breaking in repeated detachment/attachment operationsto the rotary shaft because the ceramic is considered to be low instrength, the 23rd embodiment eliminates the necessity for detaching andattaching the turntable for cleaning. The durability is effectivelyimproved.

FIG. 67 is a sectional view indicating the constitution of a highfrequency heating apparatus according to a 24th embodiment of thepresent invention.

The electromagnetic waves emitted from the magnetron 2 heat the food 6on the turntable 1 in the heating chamber 4 via the waveguide 3. Theelectromagnetic waves from the magnetron 2 are diverged from a firstwaveguide 3A to waveguides 3B and 3C at a diverging point 169 andtransmitted to the heating chamber 4 through openings 169A and 169B atthe bottom face of the heating chamber 4. In this case, adjacent partsof wall faces of the waveguides 3B and 3C are constituted of a commonmetallic plate. A diverging point 168 is formed at a node in the firstwaveguide 3A where the electric field is weak. A wall face 170 of thefirst waveguide 3A facing the antenna 30 of the magnetron 2 is projectedto increase a distance from the antenna 30. Meanwhile, no projectionlike the antenna 30 is present in the waveguides 3B and 3C and thereforethe waveguides 3B and 3C can be separated little, i.e., reduced insectional area as compared with the waveguide 3A. Accordingly, theconstitution saves the space in spite of the presence of a plurality ofwaveguides. A sectional area of the first waveguide 3A is increased bythe wall face 170 based on the sectional area of the waveguide 3B, 3C asa reference. A length of the waveguide 3B, 3C from the diverging point168 to a terminal end is approximately an integral multiple of half theguide wavelength λg and a width of the diverging point 168 is not largerthan 1/4 the guide wavelength λg, which will be more fully describedlater with reference to FIG. 68.

A metallic shielding part 171 is moved by a driving part 172 betweenopenings 169A and 169B while held in contact with the heating chamber 4and projecting parts 173 on the waveguides 3B and 3C, thus switching theopenings 169A and 169B to transmit the electromagnetic waves easily. Aseal part 174 prevents the electromagnetic waves from leaking outsidethe heating chamber 4 and the waveguide 3 irrespective of the positionof the shielding part 171.

The control means 19 controls, based on detection signals from thetemperature sensor 26 detecting the temperature of the food 6, weightsensor 23 connected to the turntable 1 and detecting the weight of thefood 6 and photosensors 61, 62 detecting the shape of the food 6, theemission of electromagnetic waves from the magnetron 2, the operation ofthe fan 27 for cooling the magnetron 2, the operation of the drivingpart 172 for moving the shielding part 171, the operation of the motor22 for rotating the turntable 1, and the operation of a driving part 175for changing a height of the turntable 1. Particularly, the controlmeans 19 controls to move the shielding part 171 when the magnetron 2does not emit the electromagnetic waves. When the heating is completed,the control means 19 controls the position of the shielding part 171 orthe height of the turntable 1 so as to obtain the best heatingdistribution and best heating efficiency to the light-weight food 6. Atthe heating time of any purpose, when the food 6 is started to beheated, the control means 19 controls to quickly generateelectromagnetic waves and also controls not to take in or to neglect theoutputs of the detection part, (e.g., weight sensor 23) which possiblymalfunctions when the electromagnetic waves are instable immediatelyafter the heating is started and before the detection part is stabilized(i.e., at a rise time). Moreover, depending on the kind of the food 6(specially a large amount of food), the control means controls to changethe position of the shielding part 171 or the height of the turntable 1a plurality of number of times in the middle of heating, therebyoptimizing the heating distribution and heating efficiency.

When the position of the shielding part 171 is changed by the drivingpart 172, the plurality of openings 169A and 169B are switched to changethe electric field distribution in the heating chamber 4. Since theposition of the shielding part 171 can be set freely in accordance withsignals from the detection parts, the proper electric field distributionis obtained to fit the heating purpose. Although not shown in FIG. 67,if a reference point is set somewhere to correctly determine theposition of the shielding part 171, the position of the shielding part171 can be managed with ease by a moving distance from the referencepoint.

When a height h of the turntable 1 is changed by the driving part 175,the height of the food is consequently changed, whereby the heatingdistribution of the food 6 is changed even with the same electric fielddistribution. Similarly, if the height h of the turntable 1 is adjustedoptimally in response to signals from the detection parts and inaccordance with a difference of the electric field distribution by theposition of the shielding part 171, the heating distribution is moreproperly arranged in conformity with the heating purpose. The height ofthe turntable 1 can be controlled by a reference point (not shown) and amoving distance, similar to the position of the shielding part 171.

The heating in the concentric direction of the food 6 seen from therotational center of the turntable 1 is generally made uniform byrotating the turntable 1. The turntable can be freely rotated or stoppedor changed in speed by the motor 22. For instance, when the temperaturesensor 26 detects the temperature irregularity in the food during theheating, the heating distribution is changed by the shielding part 171or the driving part 175 to search for a state to solve the temperatureirregularity, and the rotation of the turntable is stopped ordecelerated when the state is detected. The temperature irregularity canhence be eliminated quickly.

FIG. 68 is a sectional view showing the constitution of an essentialpart of a high frequency heating apparatus in a 25th embodiment of thepresent invention. The electromagnetic waves supplied from the antenna30 of the magnetron 2 to the waveguide 3A generate strong electricfields (antinodes 176) and weak electric fields (nodes 177) every 1/4the guide wavelength λg after showing the maximum intensity (antinode176) at the antenna 30, to be transmitted to the right and left of FIG.68. Since right and left end faces of the waveguide are arranged tocorrespond to nodes of the electric field, the electric field in eachwaveguide 3B, 3C orderly repeats antinodes 176 and nodes 177. The guidewavelength λg is determined by a distance I in a widthwise direction inFIG. 68. Therefore, a degree of freedom is allowed to a distance J1 in avertical direction, whereas a certain distance should be secured betweenthe antenna 30 and the opposite wall face 170 in case of an abnormalstate, e.g., discharging or the like brought about if the distance istoo small (not larger than 5 mm). The diverging point 168 is formed tobe the node 177 in the middle of the waveguides 3A and 3C so as toprevent the electric fields in the waveguides 3A and 3C from beingdisturbed, because an electric field 178A is generated to hold thereinthe diverging point 168 which is an opening for the electromagneticwaves. The electromagnetic waves transmitted from the diverging point168 into the waveguide 3B similarly generate an electric field 178B tohold the diverging point 168 therein and are transmitted right and leftwith the same guide wavelength λg because of the same distance I in thewidthwise direction in FIG. 68. Since a distance from the divergingpoint 168 to a right end face 179 is set to be 1/2 λg and a distance toa left end face 180 is set to be 2/2 λg, the electric field in thewaveguide 3B repeats antinodes 176 and nodes 177 orderly. Moreover,since no projecting part like the antenna 30 is present in the waveguide3B, a distance J2 in the vertical direction can be reduced so much asnot to bring about discharging between wall faces. The sectional area ofthe waveguide 3B is reduced to half or smaller by setting J2<J1/2. If anopening distance K of the diverging point 168 is too large, theelectromagnetic waves in the waveguides 3A and 3C are disturbed from theorder state. If the distance K is too small, the energy transmitted tothe waveguide 3B is decreased. Therefore, the distance K is set to beslightly smaller than 1/4 the guide wavelength λg. Likewise, an openingdistance of the opening 169 for transmitting the electromagnetic wavesto the heating chamber 4 is set to be slightly smaller than 1/4 λg.Furthermore, the waveguides 3A and 3C are set adjacent to the waveguide3B thereby to share a wall face 181.

FIG. 69 is a perspective view of the constitution of an essential partof a high frequency heating apparatus in a 26th embodiment. (Composingelements are actually connected with each other, but indicated in aseparate state for easy understanding.)

Metallic projecting parts 173A and 173B are formed by notching in theheating chamber 4 and waveguide 3 respectively in a manner to surroundthe opening 169. (The waveguide 3 has a wall face part 182 and aprojection part 183.) The projecting parts 173A and 173B project to faceeach other. The metallic shielding part 171 is constructed to be movablebetween the projecting parts 173A and 173B in touch with the projectingparts 173A and 173B. The electromagnetic waves in the waveguide 3 aretransmitted into the heating chamber 4 only when the shielding part 171is not present over the opening 169. The waveguide 3 and the heatingchamber 4 are connected with each other so as to prevent the leak of theelectromagnetic waves outside. Particularly, the leak of electromagneticwaves in an M direction is shut by a seal part 13. The seal part 13 isformed of metal having a groove of a depth of N. Since N≈λg/4, theelectromagnetic waves are not transmitted to the M side from an uppersurface 29 of the seal part 13. Generally, the impedance of theelectromagnetic waves in the M direction (index showing how hard theelectromagnetic waves are to transmit to the M side) is changed by N.The impedance is expressed by Zin=j·Z0·tan(2 π·N/λg). When N=λg/4,|Zin|=Z0·tan(π/2)=∞ (the impedance is indefinite), and theelectromagnetic waves are never transmitted to the M side from theposition 184. This way of thinking of the impedance is the same as whena microstrip line often used in a wave seal device of the microwave ovenor the like is considered. Many other embodiments are also proposed tomake the apparatus compact (Japanese Patent Laid-Open Publication No.6-13207).

FIGS. 70 and 71 show the constitution of an essential part of a highfrequency heating apparatus according to a 27th embodiment of thepresent invention, wherein a plurality of openings 169A, 169B areswitched by one driving part 172 and one shielding part 171.

In FIG. 70, the opening 169A is opened while the other opening 169B isshut, specifically, FIG. 70(a) is a configurational sectional view andFIG. 70(b) is a view of a part below the shielding part 171 of FIG.70(a) seen from above. In accordance with the rotation of the gear-likedriving part 172, the shielding part 171 operates while keeping in touchwith the projecting part 173 between the heating chamber 4 and thewaveguide 3B, 3C, whereby the openings 169A, 169B through which theelectromagnetic waves are transmitted are switched. In this case, theopening 169A overlaps with a notch 185 of the shielding part 171 therebyto be opened, while the opening 169B is shut by the shielding part 171.

FIG. 71 shows a state where the opening 169A is shielded while theopening 169B is opened. FIG. 71(a) is a sectional view of an essentialpart and FIG. 71(b) is a view of the part below the shielding part 171seen from above. In this case, the opening 169A is closed by theshielding part 171 and the opening 169B is shifted from the shieldingpart 171 and opened.

FIG. 72 is a characteristic diagram of the high frequency heatingapparatus, namely, a Rieke diagram representing working points of themagnetron 2 which shows how the electromagnetic waves are easy to enterthe heating chamber 4. The electromagnetic waves are easiest to enter anarea 186 and become harder to outer areas. When the electromagneticwaves are difficult to enter the heating chamber, the heating efficiencyis clearly decreased to increase a loss by the generation of heat at theemission part. By way of example, in the case of switching the opening169A to the opening 169B while the electromagnetic waves arecontinuously emitted, when a working point is 187 with the opening 169Bbeing shut and the opening 169A opened, as the opening 169A and 169B arestarted to be gradually opened and closed, the working point 187 startsto move in a direction of an arrow, reaching a point 188 when bothopenings are half opened. The working point is returned to the point 187when the openings are perfectly switched. In other words, there isbrought about a state in the middle of the operation of the shieldingpart 171 that the electromagnetic waves become hard to enter the heatingchamber. In the middle of the operation of the shielding part 171, notonly the aforementioned loss at the emission part is increased, but theoscillation frequency is changed or higher harmonic noises aregenerated, or the like inconveniences take place. The present inventionsolves this problem by controlling so as not to emit electromagneticwaves from the emission part when the shielding part 171 operates.

FIG. 73 is a characteristic diagram of the embodiment, an axis ofordinate showing the high frequency output P and an axis of abscissashowing the time t. In general, because of the instable state for awhile t_(ST) after the electromagnetic waves are emitted from theemission part, noises such as higher harmonics, etc. are apt to begenerated. In order to eliminate this problem, conventionally, if adetection part not resistive to noises is employed to detect the stateof the food 6 at the initial stage of heating, the food is detectedwhile refraining the emission of the electromagnetic waves for t_(M),then electromagnetic waves are emitted for t_(ST) after the detection,and the heating reaches a stable state at t_(F), as shown in FIG. 73(a).This manner of heating is considerably inefficient due to thenon-heating time interval t_(M). In contrast, according to the presentinvention, the electromagnetic waves are emitted immediately to startheating to reach the stable state at t_(F) through t_(ST) as soon aspossible, as indicated in FIG. 73(b). The state of the food 6 at theinitial stage is detected t_(ST) +Δt later (soon after the heating statebecomes stable). Therefore, the state of the food 6 can be detectedaccurately without lowering the heating efficiency.

FIG. 74 is a sectional view showing the constitution of a high frequencyheating apparatus of a 28th embodiment of the present invention.

The electromagnetic waves emitted from the magnetron 2 heat the food 6on the turntable 1 in the heating chamber 4 via the waveguide 3. At thistime, a plurality of openings 169 for guiding the electromagnetic wavesfrom the waveguide 3 to the heating chamber 4 are covered with atransparent cover 25 made of a low dielectric loss and which is hard toabsorb electromagnetic waves. A metallic stirrer vane 189 is set as arotary body in the waveguide 3, which is driven and rotated by astepping motor 190. The stirrer vane 189 assumes various operationpatterns depending on purposes, and therefore a moving distance of thevane from a reference point is always monitored by a vane positiondetector 191. The control means 19 controls the emission ofelectromagnetic waves from the magnetron 2, driving of the steppingmotor 190 by determining the operation pattern of the stirrer vane 189or driving of the motor 22 by determining the rotation and stop of theturntable 1, based on signals from the operation panel 64 input throughthe key by the user, the weight sensor 23 or a state sensor 192including other sensors such as the temperature sensor, etc., and thevane position detector 191. The apparatus has a body cover 193 and afreely openable and closable door 194.

The plurality of openings 169 are switched by the position of thestirrer vane 189, thereby to change the heating distribution. At thesame time, the matching state can be changed. Since the position or therotation of the stirrer vane 189 is freely set in conformity with thesignal from the operation panel 64, weight sensor 23 or the other statesensor 192, the heating distribution or matching state fit to theheating purpose is attained. Moreover, since the rotation and stop ofthe turntable 1 is freely set as well, the food 6 can be uniformlyheated in the concentric direction seen from the rotational center ofthe turntable by rotating the turntable 1 or, stopping the turntable 1to improve the matching state if the food 6 is milk or soup, that is,liquid.

FIG. 75 is a sectional view taken along the line P-P' of FIG. 74.

The waveguide 3 is widened in the middle, having the stirrer vane 189installed therein. Since the opening cover 25 is transparent, theoperation of the stirrer vane 189 is seen through five openings 169.

FIGS. 76 and 77 are sectional views of high frequency heatingapparatuses in a 29th and 30th embodiments of the present invention.

The apparatus of FIG. 76 has the openings 169 only in front of thestirrer vane 189, and the apparatus of FIG. 77 has only one opening 169in front of the stirrer vane 189.

Although not shown in the drawings, the openings may be set farther thanthe stirrer vane 189 seen from the magnetron 2 depending on the shape ofthe heating chamber 4 or height of the turntable 1. Otherwise, thewaveguide 3 may be extended in a vertical direction or slantwisedirection, or a plurality of waveguides 3 may be extended in a pluralityof directions, not in one direction from the magnetron 2 to constitute aplurality of openings 169. Further, the waveguide 3 may be bent astridetwo or three of the side faces, bottom face and top face of the heatingchamber in addition to the rear face. The stirrer vane 189 may beconstituted of a different number of vanes other than four. A simpleplate or rod-like body may be used as the rotary body in place of thestirrer vane.

When milk is to be warmed, after the milk is set in the heating chamber4, the milk key 65 of the operation panel 64 in FIG. 24 is manipulatedand the start key 66 is pressed. The control means 19 judges from thesignal of the operation panel 64 that the food 6 is milk and detects theamount, shape and temperature, etc. of the milk from the signals of theweight sensor 23 and state sensor 192. A suitable position for thestirrer vane 189 is consequently determined, and the stepping motor 190is driven based on the signal from the vane position detector 191, whenthe electromagnetic waves are started to be emitted from the magnetron2. The turntable 1 is kept still at this time to stabilize the matchingstate to efficiently heat. Thereafter, the milk is heated for a timedetermined by the weight sensor 23 or state sensor 192, and the heatingis stopped when the milk becomes a suitable temperature. The milk isnaturally heated in the good distribution by the convection and moreoverin the stable appropriate matching state if the electric fields areconcentrated onto the bottom face of the milk container.

Meanwhile, when frozen meat or fish is to be defrosted, the defrost key68 is pressed after the food 6 is put in the heating chamber 4, followedby the pressing of the start key 66. The control means 19 judges fromthe signal of the operation panel 64 that the food 6 is a frozen food,detecting the amount, shape, temperature and the like data of the frozenfood based on signals from the weight sensor 23 and state sensor 192 anddetermining a suitable revolution number of the stirrer vane 189. As aresult, the stepping motor 190 is driven and rotated, and theelectromagnetic waves are started to be emitted from the magnetron 2. Atthis time, the turntable 1 as well as the stirrer vane 189 is rotated toavoid the partial concentration of electric fields as much as possible.Subsequently, the food is heated for a time determined by the weightsensor 23 or state sensor 192 and stopped to be heated when reaching anappropriate temperature (completely defrosted). The food is undesirablypartially boiled if the electric fields are concentrated and thereforethe distribution is an important factor in the case of defrosting.Because of this reason, the distribution should be taken into primaryaccount regardless of the deterioration of the efficiency.

When the food that has turned cold is to be warmed again (reheated), thestart key 66 is depressed after the food 6 is set in the heating chamber4. The control means 19 judges from the signal of the operation panel 64that the food 6 is required to be reheated, and detects the amount,shape, temperature and the like of the food from the signals of theweight sensor 23 and state sensor 192. Most characteristically, thecontrol means 19 detects whether the food 6 is liquid, solid or in themiddle state of liquid and solid. In a way for this detection, theturntable 1 is rotated initially for a short time and stopped thereby tovibrate the food 6 and a change of the vibration with time is detected.The method is based on the principle that the vibration continues for along time if the food is liquid, and stops in a short time if the foodis solid. Thereafter, a suitable operation of the stirrer vane 189 isdetermined and the stepping motor 190 is driven and rotated, whereby theelectromagnetic waves are started to be emitted from the magnetron 2.When the food 6 is liquid, similar to the case of milk, the matchingstate is stabilized to heat efficiently by holding the turntable 1still. On the other hand, if the food 6 is solid, the turntable 1 isrotated to uniform the concentric heating distribution. Further, if thefood 6 is in the middle of solid and liquid, the turntable 1 isrepeatedly rotated and stopped. The heating is continued for a timedetermined by the weight sensor 23 or state sensor 192, or stopped whenthe food reaches a proper temperature. In the case of the liquid food 6,if the electric fields are concentrated at the bottom face of the foodeven when the turntable is stopped, the heating distribution isnaturally good by the convection, and the matching state is stable andproper, thereby improving the heating efficiency.

FIG. 78 is a characteristic diagram of the heating efficiency in thisembodiment. FIG. 78 is a Smith chart indicating the matching state of aload seen from the magnetron 2. A hatched area 195 is a high efficiencyarea (where the electromagnetic waves enter the heating chamber 4 mostefficiently). When the stirrer vane 189 is rotated while the turntable 1is stopped, the heating efficiencyfor the food 6 assumes acharacteristic change of Q1-Q2-Q3-Q4-Q5-Q6-Q7-Q1- . . . . That is, thematching state is changed by the position of the stirrer vane 189. Whenthe turntable 1 is rotated with the stirrer vane 189 stopped at acharacteristic position Q6, the heating efficiency shows acharacteristic change of Q6-Q8-Q9-Q10-Q11-Q6- . . . . In other words,the matching state is changed by the rotation of the turntable 1.

In short, the matching state can be changed by the position of thestirrer vane 189 and the turntable 1.

In order to heat most efficiently, the stirrer vane 189 should bestopped at the characteristic position Q6 with the turntable 1 heldstill. Needless to say, although both of the turntable and stirrer vaneare required to be rotated in some cases for the purpose of thedistribution as when the frozen food is defrosted, both can be stoppedto achieve the optimum efficiency if the food 6 is liquid. However,since the characteristic diagram of FIG. 78 changes depending on thematerial, shape, location, temperature, etc. of the food 6, the optimumposition of the turntable 1 and stirrer vane 189 should be preliminarilystored as a database in a microcomputer of the control means 19 forevery condition of the material, shape, location, temperature, etc. ofthe food 6, or the matching state should be detected by the state sensor192 or the like. The control means 19 can accordingly execute thecontrol for optimum heating on the basis of the data from the operationpanel 64, weight sensor 23, state sensor 192, etc. and the abovedatabase.

FIG. 79 is a sectional view indicating the constitution of a highfrequency heating apparatus of a 31st embodiment of the presentinvention.

The food 6 on the turntable 1 in the heating chamber 4 is heated byelectromagnetic waves emitted from the magnetron 2 via the waveguide 3.A plurality of openings 169 are formed in the bottom face of the heatingchamber 4 so as to guide the electromagnetic waves from the waveguide 3to the heating chamber 4. The waveguide 3 has a sub waveguide 196branching at a position between the plurality of openings 169A and 169B.There are provided a seal part 197 moving up and down in the subwaveguide 196, a seal driving part 198 for driving the seal part 197 orthe transparent cover 25 formed of a low dielectric loss and which ishard to absorb electromagnetic waves. Based on signals from theoperation panel 64 input through the key by the user, weight sensor 23connected to the turntable 1 for detecting the weight of the food 6 ortemperature sensor 26 detecting the temperature of the food 6, thecontrol means 19 controls the emission of electromagnetic waves from themagnetron 2, impresses signals to the seal driving part 198 thereby tomove the seal part 197, to the motor 22 rotating the turntable 1 therebyto control the rotation of the turntable, to the height driving part 175thereby to change the height of the turntable 1, or to a fan drivingpart 199 to control the rotation of the fan 27 cooling the magnetron 2and sending the air to the heating chamber 4.

When the seal part 197 is changed in position by the seal driving part198, the plurality of openings 169A and 169B are switched thereby tochange the electric field distribution. Particularly, the position ofthe seal part 197 can be freely set in accordance with the signal fromthe operation panel 64, weight sensor 23 or temperature sensor 26, andtherefore the electric field distribution is generated suitably inconformity with the heating purpose. Although not shown in FIG. 79, areference point may be set for the seal part 197, whereby the positionof the seal part 197 is easily managed and correctly detected from amoving distance from the reference point.

When the height of the turntable 1 is changed by the table heightdriving part 175, the height of the food 6 is changed accordingly.Therefore, the heating distribution of the food 6 can be changed evenwith the same distribution of electric fields. Likewise, when the heightof the turntable 1 is adjusted optimally in accordance with a differencein electric field distribution due to the position of the seal part 197or based on the signal from the operation panel 64, weight sensor 23 ortemperature sensor 26, the heating distribution fit to the heatingpurpose is realized. Similar to the seal part 197, the turntable 1 maybe controlled by its reference position (not shown) and moving distanceto be correctly positioned in a vertical direction.

The temperature sensor 26 comprises a temperature sensor 26A whichmonitors the food 6 from above the top face of the heating chamber 4thereby to detect temperatures of a plurality of points of the food in ahorizontal direction and temperature changes, and a temperature sensor26B which monitors the food 6 from above a side face of the heatingchamber thereby to detect temperatures at a plurality of points of thefood in a vertical direction and temperature changes. The temperaturesensor 26 can hence detect the temperature distribution of nearly theentire food 6. Needless to say, the temperature distribution can bedetected if only the temperature sensors 26 are set at two pointsanywhere, even not in the horizontal and vertical directions.

Although the turntable 1 is generally rotated thereby to uniform theheating distribution in the concentric direction of the food 6 seen fromthe rotational center of the turntable 1, the rotation and stop of theturntable 1 can be freely set by the motor 22 or varied in speed. Forexample, when the temperature sensor 26 detects in the middle of theheating that a temperature irregularity is brought about, the heatingdistribution is changed by the seal part 197 or table height drivingpart 175 to search for a state whereby the temperature irregularity isresolved, and consequently the turntable 1 is stopped or decelerated inthe state. The temperature irregularity can be eliminated quickly.

Further, the fan 27 is so constituted as to cool the magnetron 2 andsend air 200 to the heating chamber 4 through an air suction port 201.Since the air 200 is hot because of the heat of the magnetron 2, the airis effective to heat the food 6 if the food 6 is cold or cool the food 6if the food 6 has high temperatures. In any case, the air 200 averagesthe ambient temperature of the food 6. A revolution number of the fan 27is increased if the temperature irregularity is large, thereby toincrease the amount of the air 200, thus further uniforming the heatingdistribution. The air 200 becomes a discharge air 202 after uniformingthe temperature of the food 6 and is let out of the heating chamber 4through a discharge port 203. The amount of the air can be increasedalso by enlarging an opening size of the air suction port 201,facilitating the flow of the air into the heating chamber 4 with the useof a guide or the like, or the like manner.

FIGS. 80 and 81 show the structure of an essential part of the highfrequency heating apparatus of the 31st embodiment. The openings 169Aand 169B are apparently switched by the seal part 197 operating in thesub waveguide 196.

In FIG. 80, the seal part 197 is pulled to the lowest end in the subwaveguide 196 subsequent to the movement of a driving shaft 204 by theseal driving part 198. The seal part 197 is obtained by covering theperiphery of a conductive member 205 with a spark prevention insulatingbody 206. The electromagnetic waves are not transmitted to a lower sidethan an end face 207 of the seal because L1≈L2≈λ/4 is satisfied. In themeantime, the impedance of the electromagnetic waves at a position 208in the vicinity of a connecting point between the waveguide 3 and thesub waveguide 196 (easiness for the electromagnetic waves coming fromthe right direction in the drawing in the waveguide 3 to run left fromthe position 208) is changed by a length L3. More specifically, theimpedance Zin=j.Z0.tan(2 π.L3/λg). When L3=λg/4 is held,|Zin|=Z0.tan(π/2)=∞ (the impedance is indefinite), and theelectromagnetic waves are never transmitted left from the position 208.

In FIG. 81, the seal part 197 is pulled up to the uppermost end in thesub waveguide 196 as a result of the movement of the driving shaft 204by the seal driving part 198. In this case, L3 is equal to 0 and|Zin|=Z0.tan(0)=0 (the impedance is 0) is held, whereby theelectromagnetic waves are readily transmitted left from the position208.

Accordingly, the opening 169 is apparently opened and closed by theposition of the seal part 197. FIGS. 80 and 81 are based on the sameconcept of the impedance as in the microstrip line, and can be embodiedinto other examples.

FIG. 82 shows a 32nd embodiment of the present invention having the subwaveguide 196 connected in a different direction. Since the subwaveguide 196 occupies a smaller width under the bottom face of theheating chamber 4 in FIG. 82 than in FIGS. 79-81, the volume ratio ofthe heating chamber to the outer dimension is increased, realizing thecompact high frequency heating apparatus.

FIGS. 83-89 are characteristic diagrams of the high frequency heatingapparatus, views of an essential part of the apparatus and a flow chartrespectively, indicating how the heating distribution is uniformed by arelation of the position of the opening 169 and height of the food 6.

FIG. 83 is a characteristic diagram of a heating distributionirregularity detected when 200 cc of milk (a cup of milk) as the food 6is heated while the electromagnetic waves are transmitted to the heatingchamber 4 through either one of the openings 169A and 169B. The height his changed during the measurement. An axis of abscissa shows numbers ofopened openings and an axis of ordinate indicates a difference ofmaximum and minimum temperatures measured at a plurality of points ofthe food. The smaller the temperature difference is, the less thetemperature distribution irregularity is generated. A curve h1 isobtained when the height is 10 mm and a curve h2 is obtained when theheight is 30 mm. From this characteristic diagram, the best condition isthat the height h of the food is 10 mm with the opening 169A opened,with the effect of the temperature difference of 0°. Since thetemperature difference is about 2-15° in the generally availablemicrowave oven, the apparatus of the embodiment achieves a remarkableimprovement. The diagram implies that it is good to concentrate theelectric fields at the bottom face of the food 6 when the food 6 isliquid. The electromagnetic waves from the opening 169A heat the bottomface of the food 6, and accordingly the heating distribution is turnedgood due to the convection of the food 6 itself. The heatingdistribution irregularity in FIG. 83 when the opening 169B is usedresults from an increased temperature at an upper portion of the food 6.When the opening is separated from the bottom face of the food 6, thatis, the height is large, the electromagnetic waves tend to enter theupper portion of the food 6 easily to cause the temperature rise at theupper portion of the food.

FIG. 84 is a sectional view of the apparatus set under the optimumcondition of FIG. 83, i.e., the height is 10 mm and the opening 169A isopened.

The key 65 in the operation panel 64 in FIG. 24 is constitutedespecially for milk. When the milk is to be warmed, after the milk isbrought into the heating chamber 4, the milk key 65 is pressed and thestart key 66 is then pressed. The control means 19 detects from thesignal of the operation panel 64 that the food 6 is milk, and judgingthe amount, shape, temperature, etc. of the milk from the signals of theweight sensor 23 and temperature sensor 26, controls properly so thatthe height h is 10 mm and the opening 169A among the plurality ofopenings 169 is opened to radiate electromagnetic waves therethrough.Within a few minutes, the electromagnetic waves are started to beemitted from the magnetron 2. Thereafter, the heating is continued for atime determined by the weight sensor 23, temperature sensor 26 or thelike and finished when the milk reaches a proper temperature. The milkis heated well with the good heating distribution in this manner.

FIG. 85 is a characteristic diagram when 100 g of sliced frozen beef asthe food 6 is defrosted. The best condition is when the opening 169A isused and the height is 30 mm. Since the temperature irregularity in thegeneral microwave oven is approximately 32-60°, the heatingcharacteristic is improved in the embodiment. The 100 g sliced beef isof a representative shape among the food 6, that is, small in height(thickness t) and light in weight.

FIG. 86 is a sectional view of an essential part of the apparatus withthe opening 169A opened to the turntable 1 at a height of 30 mm, i.e.,under the optimum condition of FIG. 85.

FIG. 87 is a characteristic diagram when 300 g of frozen sliced beef asthe food 6 is defrosted. The best condition is that the opening 169B isused and the turntable is at a height of 10 mm. Since the temperatureirregularity of the general microwave oven measured in the same manneris approximately 32-75° C., the embodiment improves the irregularity.The 300 g sliced beef is standard having a height (thickness t) and anordinary weight.

FIG. 88 is a sectional view of an essential part of the apparatus whenthe opening 169B is used and the height is 10 mm, that is, under theoptimum condition in FIG. 87.

When the user defrosts frozen meat, fish or the like frozen food, theuser depresses the defrosting key 68 and the start key 66 on theoperation panel 64 of FIG. 24 after sending the food in the heatingchamber 4. In response to the signal from the operation panel 64, thecontrol means 19 determines that the food 6 is a frozen food, anddetecting the amount, shape, temperature and the like of the frozen foodbased on signals from the, weight sensor 23 and temperature sensor 26,controls so that the proper opening 169 is selected and the properheight is set. Almost simultaneously with this, the emission of theelectromagnetic waves from the magnetron 2 is started. Thereafter, thefood 6 is heated for a time determined by the weight sensor 23 ortemperature sensor 26, or stopped to be heated when the temperaturebecomes proper (the food is completely defrosted).

If the automatic cooking is carried out without using a special key,e.g., when the food turned cold is to be warmed again (reheated), thestart key 66 is pressed after the food 6 is brought into the heatingchamber 4. The control means 19 judges from the signal of the operationpanel 64 that the food 6 is required to be reheated, and detects theamount, shape, temperature, etc. of the food based on signals from theweight sensor 23 and temperature sensor 26. What is to be most notedhere is that the control means 19 makes judgment as to whether the food6 is liquid or solid. For this judgment, the turntable 1 is rotated fora short time at the initial stage and stopped, thereby to vibrate thefood 6, and a change of the vibration with time is detected. Morespecifically, the vibration continues for a long time if the food isliquid, while the vibration disappears shortly if the food is solid.Then, the control means 19 controls so that the proper opening isselected and the proper height is set. The electromagnetic waves arestarted to be emitted from the magnetron 2 soon thereafter, with theturntable 1 rotated again to uniform the concentric heatingdistribution. The food 6 is subsequently heated for a time determined bythe weight sensor 23 or temperature sensor 26 and stopped to be heatedwhen the food reaches the proper temperature. If the food 6 is liquid,similar to the case of milk, the food can be heated naturally in a goodheating distribution due to the convection so long as the electricfields are concentrated onto the bottom face of the food.

In order to realize the uniform heating for any food 6 with eliminatingirregularities in the heating distribution at all times, data of theoptimum position of the opening 169 and the optimum height should bestored beforehand in the microcomputer of the control means 19 for everycondition such as the material, shape, location, temperature, etc. ofthe food 6. This method makes it possible for the control means 19 toexert the control for optimum heating by comparing the outputs of theoperation panel 64, weight sensor 23, temperature sensor 26, etc. withthe database.

FIG. 89 is a flow chart of an example of the above process fordetermining the optimum position of the opening 169 and the optimumheight h of the turntable 1 in the constitution of FIGS. 79-82. A step209 represents an initial state, wherein the height h is 10 mm and theseal part 197 is positioned at L3=0. In a step 210, it is detected bythe weight sensor 23 whether the food 6 is liquid, the weight m of thefood 6 is smaller than m1, or larger than m1 and smaller than m2, orlarger than m2. In a step 211, the seal part 197 is moved by the sealdriving part 198 to the proper position L3. In a step 212, thetemperature sensor 26 and the other sensor is used to detect whether theheight (thickness) t of the food 6 is larger than t1, or smaller than t1and larger than t2, or smaller than t2. In a step 213, the food 6 ismoved to the proper height h by the table height driving part 175. Inthe manner as described above, the optimum position of the opening 169and the optimum height of the turntable are determined in accordancewith the material (whether it is liquid or not), weight m, height(thickness) t of the food 6.

FIG. 89 indicates sequences when the proper position of the opening 169and the proper height h of the turntable in the initial state aredetermined. The position of the opening 169 and the height of theturntable 1 may suitably be changed several times to feedback statechanges of the food 6 (particularly, temperature changes of the food asthe heating proceeds), thereby to eliminate the heating distributionirregularities.

The position of the opening 169 or the height h of the turntable 1should be changed to attain the optimum heating distribution if theweight of the food 6 is different even when the food 6 is of the samematerial, as discussed before.

According to the present invention, every time the heating is finished,the opening 169A is selected and the height h is set to be 30 mm, inother words, the apparatus is set ready for a light-weight food 6 inorder to prevent the heating distribution from not being improved in ashort time because the light food requires merely the short heating timeor prevent the short heating time from being lengthened if the heatingis started with the poor heating efficiency. On the contrary, when thefood 6 is heavy-weight, a long heating time is required, allowing theopening and the height to be changed. When the food 6 is actuallyheated, the emission of the electromagnetic waves from the magnetron 2and the rotation of the turntable 1 are started, and the amount, shape,temperature, etc. of the food are detected from signals of thetemperature sensor 26, weight sensor 23 or the other state sensor 192(for example, photosensors 61, 62) in the middle of heating. Since theapparatus is set ready for heating the light-weight food 6 at theinitial stage, if the food 6 is judged to be a large amount, the opening169 and the height h are controlled and changed suitably, and thereafterthe heating is conducted for a time determined and set by the user andstopped when the food becomes the proper temperature determined by thesensors.

FIGS. 90-95 are diagrams resulting from simulations of electric fieldsinside the high frequency heating apparatus.

FIG. 90 is a perspective view of the high frequency heating apparatus ofone embodiment. The electromagnetic waves are excited and oscillatedfrom the antenna 30 of the magnetron 2.

FIGS. 91 and 92 are perspective views along the line S-S' of FIG. 90obtained when the distribution of electric fields in the high frequencyheating apparatus (without the food) is simulated. The electric fieldsgenerated at a resonant state are indicated by equal intensity lines.(The electric field is intense, i.e., antinode where the tree ring-likepattern is thick.) These drawings represent that the electric fielddistribution is different by the position of the opening 169.

Only the first opening 169A is opened in FIG. 91. There are fourantinodes in the X direction, three antinodes in the Y direction and oneantinode in the Z direction in the heating chamber 4.

In FIG. 92, only the opening 169B is opened and, five antinodes in the Xdirection, one antinode in the Y direction and one antinode in the Zdirection are generated.

FIG. 93 is a perspective view of the flat food 6 such as shaomais or thelike heated in the high frequency heating apparatus of FIG. 90.

FIGS. 94 and 95 are perspective views along the line U-U' of FIG. 93resulting from simulations of the distribution of dielectric losses whenthe electromagnetic waves are supplied to the food over the firstopening 169A of the high frequency heating apparatus of FIG. 90. Theloss is larger and the temperature is more increased at hatched parts.

FIG. 94 is obtained when only the first opening 169A is opened, and thefood 6 is heated at a central bottom portion 214.

FIG. 95 is obtained when only the second opening 169B is opened, wherebythe food 6 is heated at end portions 215.

The cause for the electric field distribution as in FIGS. 91 and 92 willbe depicted now.

The propagation of electromagnetic waves in the waveguide 3 will befirst described.

FIG. 96 is a sectional view showing the constitution of an essentialpart of the high frequency heating apparatus, specifically, only themagnetron 2, waveguide 3, heating chamber 4 and opening 169 are shownfor the sake of brevity. A distance L4 between the antenna 30 of themagnetron 2 and a center 216 of the opening 169 is an odd multiple ofλg/4 supposing that λg is a wavelength (guide wavelength) of theelectromagnetic waves transmitted left in the waveguide 3. This distanceis selected because the electromagnetic waves are propagated left inFIG. 96 while repeatedly changing the intensity based on the guidewavelength λg determined by the shape of the waveguide 3 and theelectric field becomes always weak at a position of an odd multiple ofλg/4 (Phases of the magnetic field and electric field agree with eachother in the propagation within the waveguide, so that the magneticfield is weakened). L4 is set here to be λg×9/4. A solid arrow indicatesa direction of the intense electric fields. The electric field (as wellas the magnetic field) is inverted in direction every λg/2, andtherefore the direction of the arrow is inverted every λg/2 as away fromthe antenna 30. Both the electric field and the magnetic field areinverted with a frequency of 2.45 GHz. Since the opening 169 connectsthe heating chamber 4 to the waveguide 3 at a position where theelectric field (as well as the magnetic field) is weak in FIG. 96, theelectric fields in the waveguide 3 are not disturbed and theelectromagnetic waves are efficiently introduced into the heatingchamber 4. The opening 169A is connected to the heating chamber 4 wherethe electric field as well as the magnetic field is weak, and theopening 169B is connected to the heating chamber 4 where the electricfield (as well as the magnetic field) is intense in FIG. 79 in order tosmoothly guide the electromagnetic waves into the heating chamber 4through the opening 169A and prohibit the electromagnetic waves fromentering through the opening 169B when the seal part 197 is at theposition L3=0. On the contrary, when L3 is λg/4, the electromagneticwaves are not transmitted to the opening 169A and eventually broughtinto the heating chamber 4 only through the opening 169B. Accordingly,the openings 169A, 169B can be switched apparently by changing theposition of the seal part 197.

In the conventional example of FIG. 4, end faces 14 of the two subwaveguides 13 confronting the openings 5 are moved thereby toindependently open and close the openings 5. According to the presentinvention, the opening 169A is constituted where the electric field isweak and the opening 169B is formed where the electric field is strong,with the seal part 197 interposed therebetween. Therefore, even withonly one seal part provided in the apparatus, the openings 169A and 169Bcan be changed over.

Referring to FIG. 96, the guide wavelength λg of electromagnetic wavespropagated in the waveguide 3 is defined by the following expression (4)supposing that a width of the waveguide 3 is C, a depth of the waveguide3 is D, the number of strong and weak ridges of the electromagneticwaves in the widthwise direction is m, the number of strong and weakridges of the electromagnetic waves in the depthwise direction is n, anda wavelength λ of the electromagnetic waves in vacuum is approximately122 mm:

    λg=λ/√ [1-λ.sup.2 {(m/2C).sup.2 +(n/2D).sup.2 }](4)

In general, m=1 and n=0 and consequently an expression (5) is held:

    λg=λ/√ {1-λ.sup.2 (1/2C).sup.2 }(5)

Specifically, when C=80 mm and D=40 mm, λg is approximately 188 mm (allare inside dimensions excluding the thickness of plates of thewaveguide).

The resonance of electromagnetic waves in the heating chamber 4 will bedescribed below.

In FIG. 96, strong electric fields 217, 218 (shown by solid arrows)directionally opposite to each other are generated to hold the opening169 therebetween, so that the electromagnetic waves in the heatingchamber 4 become stable in a resonating state in a manner to be weakened(nodes) at the opening 169. The electromagnetic waves enter the heatingchamber 4 most efficiently at this time (however, the electric field isshifted 90° from the magnetic field in the resonating state, unlike inthe transmitting state in the waveguide 3).

While the resonating state is determined by the shape of the heatingchamber and the position of the opening, referring to FIG. 91 showingthe electric field distribution in the heating chamber 4, four strongelectric fields in the X direction, three strong electric fields in theY direction and one strong electric field in the Z direction aregenerated in the heating chamber, which are antinodes of the electricfields resulting from that the electromagnetic waves are distributed asstanding waves in the heating chamber because of the resonating state. A"mode" is denoted by the number of antinodes. Supposing that a size ineach direction of the heating chamber 4 when represented in threedimensions is designated by x, y and z, a mode when the antinodes of theelectric fields in respective directions are m, n and p is designated by(mnp). In the instant embodiment, a center position of the first opening169A is generally in agreement with a center position in the x and ydirections of the bottom face of the heating chamber 4, and moreover,strong electric fields are generated to hold the opening 169therebetween (to form the node at the opening 169A). Therefore, an evennumber (m: even number) of antinodes is apt to generate in the xdirection and an odd number (n: odd number) of antinodes is easy togenerate in the y direction. The other modes are hard to generate. It isreadily understood that FIG. 91 represents a mode (431) and FIG. 92 amode (511).

In summary, the electric field distribution (namely, heatingdistribution) is changeable by the position of the opening 169.

The heating chamber 4 is regarded as a hollow resonator when the heatingchamber 4 is a parallelepiped without the food 4 therein. A potentialmode is obtained from the size of the heating chamber 4 and the positionof the opening 169. The number of modes estimated to rise in eachdirection of the heating chamber 4 of dimensions x, y and z(mm) is acombination of m, n and p satisfying an expression (6) wherein m, n andp are integers:

    1/λ.sup.2 =[m/2x].sup.2 +[n/2y].sup.2 +[p/2z].sup.2 (6)

On the other hand, when the food 6 is present, a shift from theexpression (6) is caused due to influences of a wavelength compressionby the dielectric constant of the food. Experiments demonstrate,however, that a mode satisfying the expression (6) tends to take placein the vicinity of the opening 169 even when the food 6 exists in theheating chamber, and the mode is apt to be disturbed at a positionseparated from the opening 169. Therefore, for obtaining the mode (431)when λ is approximately equal to 122 mm, dimensions of, e.g., x=330 mm,y=300 mm and z=215 mm satisfying the expression (6) are selected.

In the present invention, since the opening 169 should be arranged inthe vicinity of the food 6 in order to obtain the heating distributiontargeting the food 6, the plurality of openings 169A, 169B generatingdifferent electric field distributions are formed at the nearest sideface of the heating chamber 4 to the food 6, i.e., bottom face of theheating chamber 4.

FIG. 97 is a sectional view of a high frequency heating apparatusaccording to a 33rd embodiment of the present invention.

In FIG. 97, the electromagnetic waves from the magnetron 2 heat, throughthe waveguide 3, the food 6 on a plate 219 in the heating chamber 4.Openings 169C and 169D connect the waveguide 3 with the heating chamber4 thereby introducing the electromagnetic waves to the heating chamber.The first opening 169C is formed at the center of the heating chamber 4and the second opening 169D is formed closer to the magnetron 2, so thatthe weak parts (nodes) of the electric fields of the electromagneticwaves propagated in the waveguide 3 are connected with the weak parts(nodes) of the electric fields of the electromagnetic waves distributedas standing waves in the heating chamber 4. In the meantime, an openingshielding part 220 is formed to cover the openings 169C and 169D so asto improve the heating efficiency and heating distribution for the food6. The opening shielding part 220 is like a disc consisting of a wavepermeable part 221 formed of material of a low dielectric loss and whichis hard to absorb electromagnetic waves and a wave shielding part 222formed of metal. The opening shielding part 220 is rotated by a rotaryshaft 223 made of material of a low dielectric loss and which is hard toabsorb electromagnetic waves. The rotary shaft 223 penetrating theheating chamber 4 and the waveguide 3 at a position between the openings169C and 169D is connected to and rotated by a motor 224 as a drivingpart. As the motor 224 rotates, namely, the rotary shaft 223 rotates,the position of the opening allowing the electromagnetic waves to passfrom the waveguide 3 to the heating chamber 4 is apparently changed, inother words, the first and second openings 169C and 169D are switched,whereby the electric field distribution is changed. The rotary shaft 223is connected to a first gear 225, transmitting a rotational force to asecond gear 226 via the first gear 225. The second gear 226 connected tothe turntable 1 uniforms the concentric heating distribution seen fromthe rotational center of the turntable by rotating the food 6. Thenumber of teeth of the second gear 226 is made different from that ofthe first gear 225, more specifically, the second gear 226 has a largernumber of teeth than the first gear 225 in the embodiment. Inconsequence of this, the heating distribution is uniformed better. Ashape recognition sensor 227 recognizes the shape of the food 6 andsends signals to the control means 19 which in turn controls theoperation of the magnetron 2, motor 224 or fan 27 cooling the magnetron2. In this case, an optimum power feed method (such as a switchingpattern for the openings 169C and 169D, an emission pattern ofelectromagnetic waves by the magnetron 2 or the like) is set beforehandcorrespondingly to the shape of the food, and switched in accordancewith the signal from the shape recognition sensor 227. Moreover, theopening shielding part 220 is coated with the cover 25 for the sake ofsafety and the turntable 1 is held by supporting parts 228.

FIG. 98 is a sectional view taken along the line V-V' in FIG. 97.

A center of the first opening 169C is located at the central part (bothin the longitudinal direction and in the lateral direction) of thebottom face of the heating chamber 4. The second opening 169D is formedcloser to the magnetron 2 than the first opening 169C. The openings 169Cand 169D are rectangular, while having respective four sides parallel tothe same rectangular bottom face of the heating chamber 4.

FIG. 99 is a sectional view taken along the line W-W' in FIG. 97.

The opening shielding part 220 covers the openings 169C and 169D, havingthe semi-circular wave shielding part 222 arranged over the circularwave permeable part 221, and is rotated by the rotary shaft 223. In FIG.99, the electromagnetic waves in the waveguide 3 are difficult to enterthe heating chamber 4 through the first opening 169C because of theshielding part 222, but easy to enter from the second opening 169D.Meanwhile, when the rotary shaft 223 rotates half, the electromagneticwaves in the waveguide 3 become easy to enter the heating chamber 4 fromthe first opening 169C, and difficult to enter the heating chamber fromthe second opening 169D. Therefore, the openings 169C and 169D areapparently switched by the rotation of the opening shielding part 220.

According to this 33rd embodiment, both the opening shielding part 220and the turntable 1 are rotated by one rotary shaft 223. Needless tosay, however, the opening shielding part and turntable may berespectively provided with separate rotary shafts to more efficientlyuniform the heating distribution. Although the opening shielding part220 is rotated within the heating chamber 4, the shielding part 220 maybe linearly moved right and left in the waveguide 3. Furthermore,although it is simplest if the motor 224 is an AC motor rotating at aconstant speed, a stepping motor may be employed to control and uniformthe heating distribution more delicately. The second opening 169D may beformed at the other side face of the heating chamber 4 than the bottomface of the heating chamber. Moreover, although the apparatus iscontrolled based on the signal from the shape recognition sensor 227,the detection part may be constituted of the other sensing means.

FIG. 100 is a diagram showing how the electric fields are bent when theflat food 6 (low in height) is placed in the vicinity of the center ofthe heating chamber 4 (i.e., above the first opening 169C). The food 6pushes to bend a pair of directionally opposite strong electric fields229 and 230 holding the opening 169C therebetween, with generating aninternal strong electric field 231. As a result, the food is heated bythe internal strong electric field 231 and the electric power P of theexpression (1) by the dielectric constant of the food 6. At this time, aheat generation portion 232 is brought about at a central lower part ofthe food 6, and therefore the interior of the food 6 is heated withoutan edge of the food boiled, resulting in the same distribution of thedielectric loss as shown in FIG. 94. However, FIG. 100 accompanies aperfectly contrary problem to that inherent in the conventionalmicrowave oven, in other words, the central lower part of the food 6 isheated too much whereas the edge of the food is cold. For solving thisproblem, the opening 169 is switched between the openings 169C and 169Dto uniform the heating distribution. The edge portion of the food 6becomes hot unless the using opening is at the center of the bottom faceof the heating chamber 4 (immediately below the food), probably becausethe electric field distribution in the heating chamber 4 is disturbed bythe food 6 itself when the opening at a position other than the centerof the bottom face of the heating chamber is used, and the electricfields are generated only in a direction to cover the edge portion ofthe food separated from the opening. Although the electric fielddistribution is also disturbed as it is far away from the opening 169Cat the center of the bottom face of the heating chamber 4 (immediatelybelow the food), the strong electric fields 229, 230 are kept stable inthe vicinity of the opening 169C and therefore the interior of the food6 is heated without boiling the edge portion. (Although FIG. 100illustrates that only a strong electric field deformation part 233 isdisturbed, the electric field distribution may be disturbed so much asto make four strong electric fields 234 at the top face of the heatingchamber 4 to three or two in an extraordinary case.) Since the food isgenerally placed at the center of the heating chamber 4, the firstopening 169C should be set at the center of the bottom face of theheating chamber 4, but the position of the second opening 169D may bedetermined with some degrees of freedom.

FIGS. 101-104 are sectional views of the heating chamber 4 explaininghow differently the electric fields are generated depending on theposition of the opening at the wall face of the heating chamber.

In order to obtain the mode in compliance with the expression (6)supposing that the heating chamber 4 is a hollow resonator, the openingshould be positioned as indicated in FIGS. 101-103. (Here, the openingis shown in the second dimension for the sake of brevity.)

In FIG. 101, strong electric fields 235, 236 opposite to each other aregenerated to hold an opening 169E therebetween, i.e., a mode (22*) isformed. A mode of (an even number, an even number, *) as described aboveis easily generated.

FIG. 102 shows a case where strong electric fields 237, 238 opposite toeach other are generated to hold an opening 169F therebetween, togenerate a mode (23*). The same mode as described above consisting of(an even number, an odd number, *) or (an odd number, an even number, *)is similarly easily conceivable.

FIG. 103 shows a case where strong electric fields 239, 240 opposite toeach other and holding an opening 169G therebetween are generated toachieve a mode (33*). The same mode as described above consisting of (anodd number, an odd number, *) is easily obtained in the same manner.

On the other hand, although the configuration in FIG. 104 tries toobtain strong electric fields 241, 242 opposite to each other andholding an opening 169H therebetween, a mode in compliance with theexpression (6) is not gained, making it impossible to estimate theelectric field distribution. The reason for this is that the wall facesof the heating chamber 4 are not parallel to the opening 169H.

As is made clear from the above, the electric fields can be generated asrequired if the opening 169 is provided in parallel to the wall faces ofthe heating chamber 4.

FIG. 105 is a characteristic diagram of the heating efficiency in a 34thembodiment of the present invention, more specifically a Smith chartshowing a reflection state (matching state) seen from the magnetron 2. Ahatched part is the high efficiency area 195 (where the electromagneticwaves most efficiently enter the heating chamber 4). In FIG. 105, theheating chamber and opening are matched so that a reflectioncharacteristic point 243, 244 is in the high efficiency area 195 whenonly the first, second opening 169C, 169D is opened to obtain a ratedoutput. Accordingly, the uniform heating is achieved and the heatingefficiency is enhanced as described above.

FIG. 106 is a plan view of shaomais 245 on the plate 219 as arepresentative example of flat food, seen from above. When the shaomaisare heated in the conventional microwave oven as shown in FIG. 1, acharacteristic diagram of FIG. 107 is obtained. An axis of abscissa isthe time while the shaomais are left after finished being heated and anaxis of ordinate is the temperature. An average temperature of fourshaomais at a central part 246 (hatched part) of the shaomais 245 is X1,and an average temperature of 12 shaomais at a peripheral part 247(without hatches) of the shaomais 245 is X2. Therefore, the peripheralpart 247 is hotter than the central part 246, which is a characteristicof the conventional microwave oven that the flat food like shaomais isheated only at the edge portion, and hardly heated at the centralportion.

FIG. 108 is a characteristic diagram of the temperature irregularitywhen 16 shaomais 245 of FIG. 106 are heated in the high frequencyheating apparatus of the present invention. The time while the shaomaisare left after the heating is finished is indicated on an axis ofabscissa and the temperature is shown on an axis of ordinate in FIG.108. The average temperature of four shaomais at the central part 246 isalmost equal to the average temperature X2 of 12 shaomais at theperipheral part 247, and therefore the heating is made more uniform inthe present invention.

However, the characteristic of FIG. 108 is not always achieved even ifthe heating chamber is matched with each of a plurality of openingsindependently. Although it is true that the first and second openings169C and 169D tend to heat the central part 246 and peripheral part 247respectively, the temperatures at the parts 246 and 247 do not alwaysrise at the same speed. For instance, as shown in FIG. 109, the averagetemperature X1 of the central part 246 may be higher than the averagetemperature X2 of the peripheral part 247 (inverted from theconventional characteristic diagram of FIG. 107), because the centralpart 246 holding only four shaomais may increase the temperature morequickly than the peripheral part 247 with 12 shaomais even if the sameamount of electromagnetic waves are brought into the heating chamber 4from the openings 169C, 169D. As such, the temperature rise at thecentral part is adapted to be balanced with that at the peripheral partin 35th through a 37th embodiments of the present invention describedbelow with reference to FIGS. 110-113.

In the 35th embodiment in FIG. 110, an opening area of the first opening169C is made smaller than that of the second opening 169D, differentfrom the constitution in FIG. 98, thereby to reduce the amount ofelectromagnetic waves entering the heating chamber 4 through the firstopening 169C. According to this arrangement, the temperature rise at thecentral part is restricted and the characteristic of FIG. 109 isoptimized and turned to the characteristic of FIG. 108.

According to the 36th embodiment, the reflection state (matching state)at the first opening 169C is shifted, as exemplified in a characteristicdiagram of FIG. 111 which is different from FIG. 105. While thecharacteristic point 244 is maintained in the high frequency area withthe second opening 169D, the characteristic point 243 with the firstopening 169C is shifted as indicated in FIG. 111. Similar to the effectaccomplished in FIG. 110, since the electromagnetic waves entering theheating chamber 4 from the first opening 169C are reduced (reflectedmore), the temperature rise at the central part is suppressed. Thecharacteristic of FIG. 109 is thus optimized to the characteristic ofFIG. 108.

In the 37th embodiment of FIGS. 112-113, a ratio of opening timeintervals of the first and second openings 169C and 169D is changed.FIG. 113 is a sectional view taken along the line Y-Y' of FIG. 112 whichis different from FIG. 97 in that the wave shielding part 222 isprovided with a shield projecting part 248 and a shield opening part249. In this case, for most of the time while the opening shielding part220 is rotated once, the second opening 169D is opened. Only when theshield projecting part 248 is above the second opening 169D and theshield opening part 249 is above the first opening 169C, the firstopening 169C is opened. As a result, the temperature rise at the centralpart is restricted and the temperature rise at the peripheral part ispromoted, so that the characteristic of FIG. 109 is optimized to thecharacteristic of FIG. 108.

Although not shown in the drawings, a stepping motor may be used as themotor 224 not to rotate the opening shielding part 220 constantly toshorten a time for switching the openings 169C and 169D to be opened andclosed. For example, even when either one of the characteristic points243, 244 of the openings 169C, 169D is realized as in FIG. 111, it ishighly possible that the electromagnetic waves are increasinglyreflected when the openings are switched (for instance, when theopenings 169C, 169D are respectively half opened), with decreasing theheating efficiency. Therefore, the opening shielding part 220 may bedriven at high speeds only at the switching time so as not to lower theheating efficiency.

In the foregoing embodiments, how the heating efficiency is improved andhow the heating distribution is uniformed are discussed for the flatfood. However, there are various kinds of food in a variety of shapes,and also influences of the plate should be taken into consideration.Therefore, the opening time of the openings 169C, 169D may be changeddepending on the food to be heated, or the like measures may be arrangedto achieve the optimum heating distribution, not limited to the aboveembodiments.

Referring to the local heating, the embodiments are directed to heatingof food of a relatively small size, for example, thawing of shaomais orsliced beef, etc. The present invention is not restricted to this, andapplicable to local heating to a wide area, e.g., of a tuna by switchinga central portion and an outside portion of the tuna.

The high frequency heating apparatus according to the present inventionexerts the following effects.

The local heating means can heat an optional portion of the object to beheated. Therefore, the total heating distribution is uniformed and, theportion to be heated and the portion not to be heated can be surelydistinguished.

When the protecting means is provided for protecting the local heatingmeans between the object to be heated and the local heating means, whilethe optional portion of the object is not obstructed from heating in anycase, such inconveniences that the local heating means malfunctions whenhit by scums of the object, the direction of the electromagnetic wavesis affected when scums of the object absorb the electromagnetic waves,etc. are eliminated. The target portion is stably locally heated.

When the local heating means is positioned lower than the stage and theprotecting means is between the stage and the local heating means, thelocal heating means is protected also by the stage. If the local heatingmeans is positioned always at a position close to the object to beheated, the electromagnetic waves are directly radiated to the targetportion of the object without being reflected at other wall faces. Thelocal heating is more effectively carried out.

If the protecting means loads thereon the object to be heated and thelocal heating means is placed lower than the protecting means, theprotecting means serves also as the stage or the protecting means can beformed in one body with the stage, whereby the constitution of theapparatus becomes simple with a reduced number of parts. Accordingly,the apparatus can be made compact in size, light in weight andinexpensive.

If the protecting means is provided at least partly with a dielectricbody, the local heating means is protected by the dielectric body andthe electromagnetic waves from the local heating means are emittedthrough the dielectric body to the heating chamber. The target portioncan thus be locally heatedly easily.

When the local heating means includes the waveguide part for guiding theelectromagnetic waves emitted from the wave emission means and theemission part for emitting the electromagnetic waves guided by thewaveguide part to the heating chamber, and a distance for theelectromagnetic waves to run from the wave emission means to theemission part is made approximately constant at all times, the impedanceof the electromagnetic waves is constant from the wave emission means tothe emission part. Therefore, the matching state is easy to maintainthereby to keep the heating efficiency high irrespective of how thelocal heating means is controlled. The high heating efficiencyeventually shortens the heating time and saves energy.

Supposing that the distance for the electromagnetic waves to run fromthe wave emission means to the emission part is nearly an integralmultiple of λg/2 when the running electromagnetic waves have awavelength of λ, the electric fields at the emission part become strong.Therefore, if the object to be heated at a is set close to the emissionpart, the object is heated considerably high level of efficiency.

When the wave coupling part of the emission part is connected to thedriving means and the driving means is controlled to rotate the emissionpart around the wave coupling part, the position where theelectromagnetic waves are emitted from the emission part can be changedby controlling the driving means, that is, a heated portion of theobject can be changed freely. The local heating is realized with ease.

When the waveguide part has the waveguide connecting the wave emissionmeans with the heating chamber and the wave coupling part is astride thewaveguide and the heating chamber, the wave coupling part works as anantenna, thereby efficiently guiding the electromagnetic waves in thewaveguide into the heating chamber. The heating efficiency isaccordingly further improved.

If a distance for the electromagnetic waves to be propagated from thewave emission means to the wave coupling part is nearly an integralmultiple of λg/2 when the running electromagnetic waves have awavelength λg, the electric fields become most intense at a position ofthe wave coupling part when standing waves are generated in the passingroute of the electromagnetic waves, and therefore the wave coupling partguides the electromagnetic waves in the waveguide to the heating chambermost efficiently.

If the emission part is provided lower than the object to be heated, theemission part is located close to the object to be heated at all times,so that the electromagnetic waves are emitted directly to the targetportion of the object without being reflected at other wall faces. Thelocal heating is facilitated.

When the stage for loading the object to be heated is inside the heatingchamber, with having a center thereof approximately agreed with a centerof the heating chamber, the stage can be large in size, making itpossible to efficiently utilize a space in the heating chamber. Alarge-size object can be loaded or many objects can be loaded on thestage, that is, the apparatus is convenient to use.

If the stage driving means is controlled so as to rotate the stagearound the center of the stage, this restricts the vertical movement ofthe stage during the rotation, thereby achieving stable driving of thestage. The target portion is locally heated easily. At the same time,the object to be heated is prevented from vibrating and becomes hard tospill out during the rotation.

If the local heating means and the stage driving means are controlledinterlockingly, the position of the local heating means to the object tobe heated can be detected and changed easily. Furthermore, the targetportion to be heated is locally heated more readily.

When the stage driving means is controlled to be decelerated or stoppedsimultaneously or approximately simultaneously when the local heatingmeans is controlled, the stage driving means and the local heating meansare maintained in an optimum positional relationship for local heatingfor a long time. The target portion is hence locally heated without failin a reduced time.

If the driving means is controlled so that the emission part is drivenin a range inside the bottom face of the heating chamber, a spacerequired for driving the emission part and a space outside the heatingchamber can be reduced. Moreover, since the electromagnetic waves arehard to leak outside the heating chamber from the driving range, aspecial sealing structure is eliminated, with the constitutionsimplified and the number of parts reduced. The apparatus can be madecompact, light-weight and inexpensive.

If the stage includes the wave shielding part made of a conductivematerial and the wave permeable part in the vicinity of the centerthereof, the object to be heated, specifically, the vicinity of thecentral bottom face of the object can be locally heated.

When the electromagnetic waves from the emission part is switched to bedirected between a direction where the object to be heated is presentand a direction without the object to be heated, it becomes possible toswitch the heating, namely, to locally heat the object by directlyradiating the electromagnetic waves to the object and to avoid the localheating and heat the object by means of the electromagnetic wavesreflected at wall faces of the heating chamber. The electromagneticwaves are concentrated or prevented from being concentrated in thismanner in accordance with the purpose of use, and therefore the heatingdistribution is more freely changed.

If the local heating means is controlled to switch the heating betweenapproximately the central bottom face of the object and approximatelythe periphery of the object, the heating distribution of the object ismade uniform in a simple manner.

If the local heating means is controlled to switch the portion to beheated of the object in two dimensions or in three dimensions, theheating distribution is yet delicately changed.

With the intermittent control means for intermittently controlling thelocal heating means, the portion to be heated of the object is switchedintermittently. The electromagnetic waves can be concentrated only to alimited portion, so that the heating distribution is more freelychangeable.

When the continuous control means is provided for continuouslycontrolling the local heating means, the portion to be heated of theobject is switched continuously. The heating is prevented from beingpartially concentrated and achieved uniformly in a wide area.

If there are the intermittent control means for intermittentlycontrolling the local heating means, the continuous control means forcontinuously controlling the local heating means and the switch controlmeans for switching the intermittent control means and the continuouscontrol means, the heating is easily switched in accordance with theheating purpose.

When the setting means which can be set by the user is installed in theapparatus and the local heating means is controlled by the settingmeans, the local heating suitable to input contents is realized.

When the apparatus is equipped with the detecting means for detecting,as a detection amount, at least one of a physical amount of the objectto be heated, a change amount of the physical amount, a physical amountindicating a state inside the heating chamber and a change amount of thestate physical amount, if the local heating means is controlled by thedetection amount of the detecting means, the appropriate local heatingin conformity with a state of the object itself or the state inside theheating chamber is achieved.

In the case where the local heating means is adapted to be controlled bythe temperature distribution detection means detecting a temperaturedistribution of the object to be heated, this control to the localheating means is based on the actual temperature data, so that theoptimum local heating is achieved.

At least one of the shape detection means for detecting a shape of theobject and the weight detection means for detecting a weight of theobject is set in the apparatus, whereby the state of the object isschematically detected without starting the heating. The local heatingis accordingly performed more efficiently without waste.

Before or after the heating is started, the area judging and controllingmeans judges where to heat with the use of at least either of the shapedetection means and the weight detection means. Therefore, the area tobe heated is detected irrespective of whether the heating is started ornot, and only the area, namely, only the object to be heated can beefficiently locally heated.

When the local heating means and the wave emission means are controlledin association with each other, the heating is controlled more minutely.That is, the electromagnetic waves are emitted only in a state ready toheat the portion to be locally heated or the electromagnetic waves arerefrained from coming out when the portion not to be locally heated isfocused.

When the local heating means is controlled after the wave emission meansis controlled to decrease its output or turn the output zero, wastefulheating to the portion not to be heated is avoided even if theelectromagnetic waves pass through the portion not to be heated beforethe local heating means is completely controlled.

The same effect as above is obtained when the wave emission means iscontrolled after the local heating means is controlled thereby toincrease the output.

If the local heating means is controlled by the position detection meansdetecting a position of the local heating means, the local heating meansis correctly controlled at the target position, whereby the localheating is carried out more accurately.

When the local heating means is controlled to a predetermined positioneither when the heating is started or when the heating is finished, itis enough to control the local heating means to a target position at thenext heating time based on the predetermined position, thus facilitatingthe position control.

The object to be heated in the heating chamber is extracted by theextraction means, and moreover a low-temperature portion of the objectis extracted by the low-temperature portion extraction means, thereby tocontrol the distribution variation means. The object is heated properlywithout a waste of the heating, thus decreasing the energy consumption.

If the low-temperature portion is extracted by the low-temperatureportion extraction means in the heating area set by the area settingmeans thereby to control the distribution variation means, various kindsof food of different optimum temperatures can be heated and cookedsimultaneously at respective optimum temperatures.

If the heating range is registered by the registration means into theregistration memory means and called up by the registration callingmeans, the apparatus becomes simple to manipulate, thereby improving theuser's convenience of using the apparatus.

When the heating position switch part is started to be controlled beforethe heating is started by the second operation key after at least one ofa kind of the object to be heated, a size of the heating output of theelectromagnetic waves, a heating time and a heating method is inputthrough the first operation key, the apparatus is already turned into astate to be able to heat the proper portion when the heating is started.Therefore, an unnecessary portion is never heated, heatingirregularities are eliminated and the heating is performed uniformly. Atthe same time, since the unnecessary portion is prevented from beingheated, the heating time is shortened, the user is not kept waiting fora long time, the heating efficiency is improved and the power is saved.If the heating position switch part is controlled before the heating isstarted, it is not necessary to control the heating position switch partin the middle of the heating and the controlling number of times isreduced. Accordingly, such problems are eliminated that the electricfields are disturbed or the reflecting waves are increased while theheating position switch part is being controlled. The wave emissionmeans is prevented from abnormally generating heat, thus enhancing thedurability of the apparatus. In addition, higher harmonics are preventedfrom being generated. Noises are restricted and the malfunction of otherparts or external devices of the high frequency heating apparatus can beprevented.

If the portion to be heated is changed in accordance with the heatingpurpose, the apparatus is so adaptable to some extent as to uniformlyheat the object or intensively heat a specific portion of the object. Byusing a microwave oven as a representative example of the high frequencyheating apparatus, a single food can be heated uniformly or many kindsof food can be selectively heated (e.g., boiled or fried stuff is heatedwhile fresh vegetables on the same plate are not heated).

If the driving part controls the local heating means to drive with aconstant cycle immediately after the heating is started and change thecycle or stop in the middle of the heating, the heating distribution inthe middle of the heating is changed from that immediately after thestart of heating. Even if a specific portion of the object is delayed inheating, this portion can be intensively heated thereafter according tothis manner of heating and therefore the object is uniformly heated.Thus, intensive concentrated heating to only the required portion isenabled.

The control part controls to hold the heating output of the waveemission means constant immediately after the heating is started andchange or stop the heating output, depending on a state of the localheating means during the heating, thereby changing the heatingdistribution immediately from a time after the heating is started to atime in the middle of the heating. Particularly, the control part canrefrain a specific portion of the object from being heated at the middlestage of the heating, and therefore a portion heated more may be stoppedto be heated to eliminate the heating irregularity thereby providing auniform heating or, a portion not to be heated may be refrained frombeing heated.

When the electromagnetic waves are guided to the heating chamber throughthe power feed chamber which is provided with the feed port switch part,if the waveguide is connected with the heating chamber via the powerfeed chamber, the electromagnetic waves are restricted not to bereflected and the waveguide is matched easily with the heating chamber.If the feed port switch part does not project in the heating chamber andis coated with a cover to prevent the user from touching, the bottomface of the heating chamber including the cover becomes flat, whichfacilitates cleaning of the heating chamber. When the local heatingmeans is covered, it is enough for the cover to cover the power feedchamber, not the whole bottom face of the heating chamber. The cover canbe small and inexpensive.

When the turntable is made of metal or a conductive material having anopening of 1/2 or larger the wavelength of the electromagnetic waves inthe rotating direction, the electromagnetic waves are allowed to passthrough the opening of the turntable up and down. The portion to beheated of the object is hence switched easily.

If the turntable is made of metal or conductive material, the turntableis employable in such structure that the heater is installed below thebottom face of the heating chamber of, e.g., a highly heat-proof,popular microwave oven with the function of a range.

If the turntable is formed of a material passing the electromagneticwaves, the electromagnetic waves pass up and down via the turntablewithout being reflected. The portion to be heated of the object can beeasily switched.

If a circle of a radius R is projected upward centering the rotationalcenter of the turntable of a radius r on the bottom face of the heatingchamber when R>r, even if the liquid object to be heated is spilt on theturntable or in the periphery of the turntable, the heating chamber canbe cleaned with good workability without detaching the turntable.

When the local heating means is controlled so that the center of theobject is heated after the heating is started and then the periphery ofthe object is heated, it is effective not to heat the edge, i.e.,periphery of the object too much, thus eliminating heatingirregularities. The elimination of heating irregularities reduceswasteful heating, enhances the heating efficiency and saves the energy.The heating time is shortened, with the user's wait time decreased.

If the electromagnetic waves are directed to the center of the bottomface of the heating chamber by the local heating means after the heatingis started, the center of the object is mainly heated. Thereafter, theelectromagnetic waves are directed to the outside of the bottom face ofthe heating chamber, whereby the periphery of the object is mainlyheated. In this method, heating irregularities are less generated.

In accordance with the output of the detection part detecting thephysical amount of the object or the state of the heating chamber, thepower feed switch part is driven before the object is partiallyoverheated. The portion to be heated is accordingly switched to therebysuppress the heating irregularities.

When the frozen object is to be defrosted, the electromagnetic waves arecontinuously emitted to heat the object when the maximum temperature ofthe object is estimated to be not higher than 0° C. The emission of theelectromagnetic waves is temporarily stopped when the maximumtemperature is estimated to exceed 0° C. In this manner of control, thetemperature difference after the maximum temperature is beyond 0° C. isrestricted not to be increased. Moreover, the temperature irregularitiesare reduced due to the thermal conduction within the object to be heatedwhile the emission of electromagnetic waves is stopped. The frozen foodis defrosted with reduced heating irregularities.

When the local heating means is driven while the electromagnetic wavesare stopped or reduced, the electromagnetic waves in the heating chamberare never stirred during the operation. Therefore, the wave emissionmeans is used in a stable operation range, so that the unnecessaryradiation of electromagnetic waves or the temperature rise of the waveemission means is restricted, making it easy to counteract noises andarrange a cooling structure.

If the local heating means is constituted of the rotary waveguide,rotary antenna or stirrer, the direction of the electromagnetic waves isswitched easily in a simple constitution and by a simple driving method.Therefore, the apparatus becomes inexpensive and reliable as is apparentfrom previous results.

When the driving part for driving the local heating means is constitutedof a stepping motor or a combination of the other motor and a switch,the position of the local heating means can be controlled correctly withease, so that the direction of the electromagnetic waves is correctlycontrolled with ease. The portion to be heated is switched moreaccurately in the simple and inexpensive arrangement of the apparatus.

If the temporary stop time, while the emission of the electromagneticwaves is suspended, is determined by the output of the detection means,a rate of the temperature rise because of the thermal conduction in theobject to be heated or a temperature difference of the object from theambient temperature in the heating chamber can be set in accordance withthe state of the object or heating chamber. The heating is properlyexecuted to restrict defrosting irregularities.

When a plurality of waveguides are made adjacent to each other, theapparatus is constituted of a small number of parts in a small space, tobe compact, light-weight and inexpensive.

If the waveguide is branched at a node of the electric field, theelectromagnetic waves are efficiently transmitted to the branchingwaveguides and further to the heating chamber through a plurality ofopenings. The good heating efficiency shortens the heating time andreduces the user's wait time. Moreover, the unnecessary consumption ofpower is fairly suppressed. The reliability is improved due to thereduced loss at the wave emission means.

When a sectional area of each of the branched waveguides is made small,the apparatus is constituted of a small number of members in a smallspace, i.e., becomes compact, light and inexpensive. Because of thebranched waveguides having a length of an integral multiple of half theguide wavelength λg and not smaller than 0, the electromagnetic wavesresonate with the guide wavelength λg also in the branched waveguides.The electromagnetic waves are accordingly transmitted efficiently intothe heating chamber through the plurality of openings.

If a width of a branching point of the waveguide branching from thefirst waveguide is set to be not larger than 1/4 the guide wavelengthλg, the resonating electromagnetic waves in the first waveguide areefficiently transmitted to the branched waveguide while maintaining theresonant state. The heating efficiency is good, because theelectromagnetic waves are transmitted to the heating chamber efficientlythrough the plurality of openings.

When the shielding part having a plurality of openings is designed toshut the openings while keeping contact with projections of either ametallic or a conductive member fixed to at least one of the heatingchamber and the waveguide, the electromagnetic waves are nevertransmitted through between the shielding part and projections and thuscompletely shut. Since the openings from which the electromagnetic wavesare emitted are correctly switched, the heating distribution can bechanged freely to be optimum for the heating purpose, that is, any foodcan be heated uniformly. Similarly, since the electromagnetic waves areprevented from leaking outside from between the shielding part andprojections, the apparatus operates safe and is prevented frommalfunctioning, without generating noises to external devices.

When the seal part having a plurality of openings is provided in amember fixed to at least one of the heating chamber and the waveguide,the electromagnetic waves are not transmitted from between the shieldingpart and openings and restricted not to leak-outside.

If the one shielding part is designed to close and open the plurality ofopenings on the same wall face, the shielding part becomes simple instructure with a small number of parts and becomes inexpensive. Even ifthe shielding part were obliged to stop by an accident, any of theopenings is always opened, thus ensuring the supply of electromagneticwaves to the heating chamber. It is prevented that every opening is shutand no electromagnetic wave is supplied to the heating chamber. The waveemission means or waveguide is hardly accompanied with an abnormal lossor an abnormal generation of heat, in other words, safety and highreliability are achieved.

When the shielding part for opening and closing the plurality ofopenings is adapted to be driven by one driving part, the driving partis rendered simple in structure with a reduced number of parts and iseasy to control. The apparatus becomes compact, light-weight andinexpensive.

When the shielding part is driven while the emission of electromagneticwaves is stopped, it is prevented that the electric fields are disturbedduring the operation of the shielding part and the wave emission meansgenerates an abnormal loss or higher harmonics. Thus, the apparatus issafe with high reliability without generating noises to external devicesor malfunctioning.

If the shielding part is set at a position suitable for the object of alight weight or for short-time heating when the heating is started orfinished, the apparatus is prepared for short-time heating for thelight-weight object, etc. every time the heating is started.Accordingly, the heating for the light object never fails. On the otherhand, when the object of a large quantity is to be heated which requiresa long time, there is enough time even when the shielding part is movedto a suitable position after the heating is started. In other words,according to the present invention, since the adequate heatingdistribution is obtained immediately after the start of heating for thelight object and the shielding part is not necessary to move so muchwhen the light object is to be heated, the power for moving theshielding part or the power loss during the operation of the shieldingpart is eliminated, thereby enhancing the heating efficiency. Theheating time is shortened. Since the driving part is controlled so thatthe object to be heated is set at the position suitable for thelight-weight object or for short-time heating when the heating isstarted or finished, the apparatus is always ready for short-timeheating for the light-weight object every time the heating is started.

If the apparatus is arranged not to take in the output of the detectionmeans or neglect the output for a while after the heating is started,the detection means is freed of wrong detections when theelectromagnetic waves are instable at the initial stage of heating andcan correctly detect in the stable state. The control based on theoutput of the detection means becomes correct, ensuring highly reliableoperation of the apparatus. Since it is unnecessary to secure aninterval to withhold the emission of electromagnetic waves after theheating is started in order to detect the initial state of the object bythe detection means, the heating is efficiently performed from thebeginning. The wait time for the user is shortened.

Depending on the output of the detection means, the shielding part isrotated a plurality of number of times from the start to the end ofheating, whereby the heating distribution is changed. The heating isthus achieved suitably to correspond to the state of the object to beheated. Any object can be heated uniformly and efficiently.

Depending on the output of the detection means, when the driving part isso controlled as to change the position of the object to be heated aplurality of number of times from the start to the end of heating, theheating distribution is changed to heat suitably correspond to the stateof the object. Any object can thus be heated uniformly and efficiently.

If the apparatus includes the driving body such as the rotary body inthe waveguide, etc. and a plurality of openings, the plurality ofopenings are switched one another by the rotation of the rotary body.The electric fields can be apparently switched delicately. The whole ofthe object is heated uniformly.

When the driving body such as the rotary body or the like is constitutedwithin the waveguide, the constitution is simple not occupying a spacethereby to maintain the effective volume inside the heating chamber tothe entire apparatus.

If the driving body is switched among a plurality of operation patternsin accordance with the input through the operation key, the electricfield distribution is changed to be optimum in accordance with theobject to be heated or the total heating sequence, different from whenthe driving body is rotated constantly. More uniform heating isachieved.

In contrast, in the case where no such sensitive electric fielddistribution as requires switching is indicated (for instance, when itis enough to simply heat the bottom face of the object to obtain theuniform distribution from the convection because the object is liquidsuch as milk or the like), the rotary body may be stopped at a positionof the best matching state. In this case, the object is heatedefficiently, and the heating time, eventually the user's wait time isshortened. At the same time, the loss is reduced and the power is saved.Further, the thermal stress at the wave emission means is decreased,increasing the reliability.

When the state of the object to be heated or inside the heating chamberis detected and the rotary body is switched among the plurality ofoperation patterns in accordance with the state, the optimum electricfield distribution fit for the state of the object is generated duringthe heating, and therefore the object is heated more uniformly.

On the other hand, if it is detected by the detection means that theobject does not require such distribution as needs switching (e.g., whenit is enough to heat the bottom face of the object to obtain the uniformdistribution from the thermal convection as the object is liquid such asmilk or the like), the rotary body can be stopped at a position of thebest matching state afterwards. Since the object is efficiently heatedin this case, the heating time, eventually the wait time for the user isshortened. At the same time, the loss is reduced to save the power.Moreover, the thermal stress at the wave emission means is reduced,whereby the reliability is increased.

Since the rotary body is rotated in the case of frozen food (at thedefrosting time), the electric fields in the heating chamber are alwayschanged and prevented from being concentrated to a part of the frozenfood. The distribution irregularity peculiar to the defrosting time thatthe food is partially boiled although the whole is frozen is avoided.

The matching state is never changed by the rotation of the stage if thestage is not rotated when milk or soup is input through the operationkey. The matching state in this case realizes the most efficientheating. The electricity for rotating the turntable becomes unnecessaryand is saved. In general, the heating distribution in the liquid objectsuch as milk, soup, etc. is less influenced by the rotation and stop ofthe turntable, and therefore distribution irregularities are notgenerated.

If the stage is not rotated when the detection means detects that theobject to be heated is liquid, the matching state is not subjected tochange by the rotation of the stage, whereby the object is mostefficiently heated. Since the electricity for rotating the stage isunnecessary at this time, the power is saved.

When the electromagnetic waves are introduced to the heating chamberthrough the plurality of openings, the electric field distribution isdifferent at every opening, so that the object is more uniformly heatedthan when there is only one opening.

If the opening is in the bottom face of the heating chamber, whichportion of the object should be heated intensely is almost determined bythe position of the opening. A target distribution is easy to form. Whenthe opening is in the bottom face of the heating chamber, the object tobe heated is relatively close to the opening and therefore the heatingefficiency is good. The heating time is reduced to thereby shorten theuser's wait time and limit the excessive consumption of electricity. Theenergy is saved and the loss at the wave emission means is reduced whichimproves the reliability.

When a position of the object in a vertical direction is changed or adistance between the object and conductive member below the bottom faceof the object is changed, the heating distribution in the object to beheated can be changed even with the same electric field distribution inthe heating chamber. The heating distribution is controlled freely.

When the plurality of openings are switched in accordance with the inputthrough the operation key or the output of the detection part to allowthe electromagnetic waves to pass through, the heating distribution isconformed to the content of the operation key or detected content by thedetection means, and uniformed.

If the electromagnetic waves are controlled by switching of the openingsand emitted from the opening closest to the center of the bottom face ofthe object to be heated if the object is liquid, the center of thebottom face of the object can be intensively heated to raise thetemperature higher than the other portion of the object. Since theobject is liquid, the thermal conduction is brought about in this caseand the temperature is naturally averaged in the vertical direction.Accordingly, the problem peculiar to the liquid object that the upperportion is overheated is eliminated and thus the object is uniformlyheated with no temperature difference in the vertical direction.

If the object to be heated is higher than a certain height or heavierthan a certain weight, the plurality of openings are switched so thatthe electromagnetic waves are hard to come out from the opening closestto the center of the bottom face of the object. The problem peculiar tothe large object that the bottom face is heated too much and scorched orthe lower portion is overheated is consequently eliminated. The uniformheating distribution without a temperature difference in the verticaldirection is realized.

When the position of the object to be heated in the vertical directionis changed or the distance between the object and the conductive memberbelow the bottom face of the object is changed in accordance with theinput through the operation key or the output of the detection means,the heating distribution is changed in accordance with the content inputthrough the operation key or the detected content by the detectionmeans. The heating distribution is optimized to meet the heatingpurpose.

In the case where the object to be heated is lower than a certain heightor lighter than a certain weight, the object is moved up or the distancebetween the object and the conductive member below the bottom face ofthe object is increased, whereby the annoying local concentration ofelectric fields which is peculiar to the small object is eliminated,thereby to achieve the uniform heating distribution.

If the seal part is made movable within the sub waveguide branching fromthe waveguide between the first and second openings among the pluralityof openings, the movement of the seal part apparently switches to selectthe opening that is easier to transmit electromagnetic waves to theheating chamber from the waveguide. That is, the heating distribution ischanged freely.

At the same time, a spark or leakage of electromagnetic waves is notbrought about when the openings are switched, with ensuring safety ofthe apparatus.

When the openings are switched by way of the movement of the seal partto one that is easier to guide the electromagnetic waves from thewaveguide to the heating chamber in accordance with the input throughthe operation key or output of the detection part, the heatingdistribution conforming to the content input through the operation keyor detected by the detection part is formed, so that the heatingdistribution of the object to be heated is made uniform.

The first temperature sensor detects temperatures at a plurality ofpoints of the object to be heated in the vertical direction ortemperature changes, and the second temperature sensor detectstemperatures of a plurality of points of the object in the horizontaldirection and temperature changes. Therefore, the temperaturedistribution of the whole object to be heated is accurately detected.

When the object to be heated is moved in the vertical direction or thedistance between the object and the conductive member below the objectis changed by detecting the temperature distribution of the object bythe temperature sensor, and if the electromagnetic waves areconcentrated to the low-temperature portion of the object or preventedfrom being concentrated to the high-temperature portion of the object,heating distribution irregularities are restricted in accordance withthe actual temperature of the object. Considerable uniform heating ishence achieved.

When the temperature distribution of the object to be heated is detectedby the temperature sensor and the opening which is easier to emitelectromagnetic waves among the plurality of openings is selected,thereby to concentrate the electromagnetic waves to the low-temperatureportion of the object or prevent the electromagnetic waves from beingconcentrated to the high-temperature portion of the object, heatingdistribution irregularities can be restricted in accordance with theactual temperature of the object, thereby achieving fairly uniformheating.

When it is detected from the output of the temperature sensor that thetemperature rise of the low-temperature portion of the object to beheated is large or the temperature rise of the high-temperature portionof the object is small, in other words, that it becomes possible toimprove the temperature irregularity, the stage is stopped to be rotatedor decelerated, whereby the heating distribution is improved quickly toeliminate the irregularity and realize considerably uniform heating.

When it is detected from the output of the temperature sensor that atemperature difference at each of a plurality of points of the object tobe heated is not smaller than a certain value, the rotating number ofthe fan part is increased, the air suction port is opened wide or theair flow is facilitated, etc. thereby to increase the amount of the airentering the heating chamber. As a result, the total ambient temperatureis averaged and moreover, the temperature is averaged due to the thermalconduction within the object to be heated, so that the distributionirregularities are eliminated.

The heating chamber is connected with the waveguide via the plurality ofopenings, and the first opening is formed at the central part of thebottom face of the heating chamber (in the longitudinal direction andalso in the lateral direction). In the constitution, the central bottomportion of the object is heated at the first opening and the edgeportion of the object is heated at the other opening. Accordingly, theobject is heated uniformly as a whole.

When every side of the rectangular bottom face of the heating chamber ismade in parallel to any one side of the rectangular opening, strongelectric fields are generated by the electromagnetic waves emitted fromthe wave emission means in opposite directions to hold the opening. Theaimed electric field distribution is calculated on the assumption thatthe heating chamber is a hollow resonator is obtained as a standing wavedistribution on the bottom face of the heating chamber. Therefore, themode in the heating chamber (at least in the vicinity of the opening) isas required, resulting in the required heating distribution of theobject.

When at least one of the plurality of openings is shielded by theopening shielding part, the standing wave distribution formed at everyopening not shielded can be switched or various standing waves aremingled. Therefore, the heating distribution of the object is switchedor combined thereby to be made uniform.

In the constitution that the matching state (rated output) is obtainedwhen other openings of the plurality of openings than an optionalopening are closed, the object can be efficiently heated even when thepower is fed from any of the openings. Therefore, the heating time, inother words, the user's wait time is shortened. The power is also saved.Furthermore, the thermal stress of the wave emission means is reducedthereby to increase the reliability.

If the opening shielding part shields the opening by rotating about therotary shaft at a position other than the central part of the bottomface of the heating chamber (both in the longitudinal direction and inthe lateral direction), the electric field distribution in the heatingchamber is stirred, so that the heating distribution of the object ismade uniform. In this case, the opening can be formed at the centralpart of the bottom face of the heating chamber, and therefore thecentral portion of the bottom face of the object can be switched to beheated or not to be heated in the simple constitution. Thus, the heatingis made more uniform.

If the opening shielding part is to shield the opening by way of therotation thereof at a constant speed, the idea is realized by thedriving part rotated at a constant speed. The electric fielddistribution in the heating chamber is changed in the simpleconstitution (the constitution which is inexpensive and easy toconstruct) to uniform the heating distribution of the object.

When the opening shielding part is shaped like a disc, the shieldingpart has no angular part. The electric field distribution in the heatingchamber is changed in this simple constitution which is inexpensive andeasy to construct, thereby to uniform the heating distribution of theobject. Because of the opening shielding part without angular parts, theopening part is less likely to be broken through contact with othercomponents, thereby enhancing in safety.

If the opening shielding part is constituted of the wave permeable partof resin or the like and the wave shielding part of metal or the like,when the position of the shielding part is changed by the driving part,the electromagnetic waves are switched to be transmitted and shut. As aresult, the standing wave distribution in the heating chamber isswitched, various standing waves are mixed or the electric fielddistribution is stirred, whereby the heating distribution of the objectis made uniform. Moreover, a spark between the opening and the waveshielding part is prevented by the wave permeable part, so that thesafety is enhanced.

Regarding an opening area of each opening, if the area of the openingclosest to the center of the bottom face of the object to be heated ismade minimum, the electromagnetic waves from the minimum opening areless than those emitted from other openings. Accordingly, influencesthat are too large on the distribution at the opening closest to thebottom face of the heating chamber and also closest to the object arelimited if the openings have the same area, with the Cw influences onthe distribution at the other openings enhanced. The heatingdistribution of the object is thus made uniform.

In the constitution that the matching state (rated output) is notattained when other openings than the opening closest to the centralbottom face of the object to be heated are shielded, the electromagneticwaves emitted at this time from the opening are reduced than from theother openings. Therefore, too large influences on the distribution, ifin the same matching state, by the opening closest to the central bottomface of the object as compared with the influences on the distributionby the other openings are restricted, thereby to increase the influenceson the distribution of the other openings. The heating distribution ofthe object is made more uniform according to this manner.

When the opening shielding part is adapted to shield the opening whileoperating at a non-constant speed, the time required for opening andclosing the opening, the opened time and the shut time can be changedfor every opening. Since the time required for opening and closing theopening or the shut time without the electromagnetic waves sent in theheating chamber is reduced, while the opened time while theelectromagnetic waves stably enter the heating chamber thereby togenerate the standing wave distribution is lengthened, the object can beheated efficiently. The heating time, namely, the user's wait time isshortened. Moreover, the power is saved and the thermal stress at thewave emission means is reduced to increase the reliability.

INDUSTRIAL APPLICABILITY

As described hereinabove, the high frequency heating apparatus of thepresent invention can heat an optional portion of the object. If heatingof the optional portion is combined with one another, the heatingdistribution of the object to be heated is uniformed. The presentinvention is accordingly suitable for use in microwave ovens or the likefor cooking various kinds of food.

We claim:
 1. A high frequency heating apparatus comprising:a heatingchamber for accommodating an object to be heated; an electromagneticwave emission means for emitting electromagnetic waves; a local heatingmeans for focusing the electromagnetic waves emitted from saidelectromagnetic wave emission means on a local portion of the object; acontrol means for controlling said local heating means to change thelocal portion of the object on which the electromagnetic waves arefocused to thereby heat a secondary portion of the object; and drivingmeans for rotating and driving said local heating means about a drivingshaft, said driving shaft being positioned at a position except a centerof a bottom face of said heating chamber.
 2. A high frequency heatingapparatus according to claim 1, wherein said local heating meanscomprises a waveguide part for guiding the electromagnetic waves emittedby said electromagnetic wave emission means, an emission part foremitting the electromagnetic waves guided by said waveguide part to saidheating chamber, and said driving means for driving said emission part.3. A high frequency heating apparatus according to claim 2, wherein saidemission part has an electromagnetic wave coupling part connected tosaid driving means, and said control means controls said driving meansso that said emission part rotates about a center of saidelectromagnetic wave coupling part.
 4. A high frequency heatingapparatus according to claim 3, wherein said waveguide part has awaveguide connecting said electromagnetic wave emission means with saidheating chamber, and said electromagnetic wave coupling part isconstituted astride an interior of said waveguide and an interior ofsaid heating chamber.
 5. A high frequency heating apparatus according toclaim 3, wherein a distance for the electromagnetic waves to run fromsaid electromagnetic wave emission means to said electromagnetic wavecoupling part is approximately constant at all times.
 6. A highfrequency heating apparatus according to claim 5, wherein the distancefor the electromagnetic waves to run from said electromagnetic waveemission means to said electromagnetic wave coupling part isapproximately an integral multiple of λg/2 when λg is a wavelength ofthe running electromagnetic waves.
 7. A high frequency heating apparatusaccording to claim 2, wherein said emission part is located lower thanthe object to be heated.
 8. A high frequency heating apparatus accordingto claim 1, wherein said local heating means has a waveguide part forguiding the electromagnetic waves emitted from said electromagnetic waveemission means, and an emission part for emitting the electromagneticwaves guided by said waveguide part into said heating chamber, andwherein a distance for the electromagnetic waves to run from saidelectromagnetic wave emission means to said emission part isapproximately constant at all times.
 9. A high frequency heatingapparatus according to claim 8, wherein the distance for theelectromagnetic waves to run from said electromagnetic wave emissionmeans to said emission part is approximately an integral multiple ofλg/2 when λg is a wavelength of the running electromagnetic waves.
 10. Ahigh frequency heating apparatus according to claim 1, furthercomprising a stage on which the object to be heated is placed, whereinsaid local heating means guides the electromagnetic waves in a directionradially of said stage.
 11. A high frequency heating apparatus accordingto claim 1, wherein said local heating means has a plurality of openingsfor guiding the electromagnetic waves to said heating chamber.
 12. Ahigh frequency heating apparatus according to claim 11, wherein saidcontrol means controls said local heating means to switch the pluralityof openings.
 13. A high frequency heating apparatus according to claim12, wherein said local heating means has an opening shielding part forshielding at least one of the plurality of openings, and said controlmeans controls said opening shielding part.
 14. A high frequency heatingapparatus according to claim 13, wherein a seal part is provided to shutelectromagnetic waves between the plurality of openings and said openingshielding part.
 15. A high frequency heating apparatus according toclaim 11, wherein at least one of the plurality of openings is formed atthe bottom face of said heating chamber.
 16. A high frequency heatingapparatus according to claim 11, wherein an opening area of each of theplurality of openings is made different.
 17. A high frequency heatingapparatus according to claim 11, wherein the plurality of openingsgenerate different electric fields on the bottom face of said heatingchamber.
 18. A high frequency heating apparatus according to claim 1,wherein said local heating means has a waveguide for guiding theelectromagnetic waves to said heating chamber and said driving meansincluding a driving body in said waveguide.
 19. A high frequency heatingapparatus according to claim 1, wherein said local heating means has afirst waveguide for transmitting electromagnetic waves emitted from saidelectromagnetic wave emission means and a plurality of waveguidesbranched from said first waveguide to guide the electromagnetic wavesinto said heating chamber.
 20. A high frequency heating apparatusaccording to claim 1, wherein said local heating means changes theposition of the object to be heated in a vertical direction.
 21. A highfrequency heating apparatus according to claim 1, wherein said localheating means changes a distance between the object to be heated and amember below the bottom face of the object to be heated.